113. How Can You Improve Your Mental Endurance?
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Vladimir Putin, have a sandwich. I'm Angela Duckworth. I'm Stephen Dubner. And you're listening to No Stupid Questions. Today on the show, can you train your brain to focus for a longer period of time? I used every single ounce of my physical and mental energy, and I have nothing left. No.

Angela, you and I have both read a new working paper by four economists, Christina Brown, Supreet Kaur, Gita Kingdon, and Heather Schofield about what's called cognitive endurance, which was a phrase that captured my attention. A good phrase, yeah. It's a very good phrase. Is there a generally accepted definition of that in the academic or psychological realm?

They defined it as, quote, the ability to sustain effortful mental activity over a continuous stretch of time. The paper makes two statements.

primary arguments. One, that students from low-income backgrounds exhibit what is called cognitive fatigue more quickly than high-income students. But point two, cognitive endurance is essentially, as I understand it at least, a muscle that anyone can build up. So because cognitive endurance sounds to me at least a lot like grit, I wanted to hear a

what you have to say about this research, what it means for anyone who would like to increase their own cognitive endurance, whether in an educational setting or otherwise. So maybe we could just start with your describing what the study actually showed, and we can take it from there. Gosh, you had me at hello. Like this title, right? Cognitive endurance as human capital is like porn for me. I can't resist. It's titillating. So here's the first line.

Schooling may build human capital not only by teaching academic skills, but by expanding the capacity for cognition itself. It's a bold claim to say maybe one of the most important reasons why we go to school is to build up this thing called cognitive endurance, the ability, as these authors say, to sustain effortful mental activity over a continuous stretch of time.

And I've been thinking about this paper since I read it a few weeks ago. They randomly assigned elementary school students in India to different conditions. In one condition, these kids were asked to do something which basically they

The experimenters, the economists here, thought was like, it's training. Like, let's give them cognitively hard stuff to do over 20 or 30 hours, and then there'll be a control group. And at the end, we'll see who has more of this cognitive stick-to-itiveness.

So it'd be the equivalent of if you're trying to train someone physically saying, I'm going to take a group of you, randomize you, split you in half, and then a bunch of you are going to do 100 pushups a day and 100 sit-ups a day over the course of a few hours. And the rest of you are just not. And then we'll go out and we'll do feats of strength and see how you do. Is it that cut and dried? Well, you know, there is not the language of like, it's a muscle, but absolutely. I think that's the mental imagery.

Can you talk about for a moment what the actual endurance building tasks were and how typical they were for an educational setting? In other words, are these the kind of things that some schools are already doing a lot and others aren't? Or are they separate from typical education tasks? So in the treatment condition, the cognitive endurance training condition, these things

kids were given 20 to 30 hours of hard cognitive work. The majority of them were doing math problems. It was on tablets. And when you get something right, it levels you up. It's almost like you go to your physical trainer and as soon as you can lift five pounds, they move you up to eight pounds or something like that. So it's getting harder as you get better.

to maintain this cognitive load. There was another cognitive endurance training condition where you did lumosity kind of games, but not lumosity. They call them non-academic games, which they describe as providing a pure test of our mechanism. In other words...

can you learn to focus and engage for a longer period? Is that what that means? Yeah. They were trying to give you cognitively challenging tasks, but not like what you usually do in elementary school. They were trying to isolate just cognitive effort by itself. You know, what's interesting to me about that second treatment and that type of task is that it does sound quite familiar to

to those of us, whether as kids or as parents or as educators, who've heard these arguments about the reason you should play a musical instrument when you're six years old, or the reason you should play sports. There are all these different functions that are not really about musicality and not really about athleticism. It's about learning skill, focus,

teamwork, commitment, on and on and on and on. So that was also interesting to me that they wrote that these non-academic games were, quote, a pure test of our mechanism because I'm very curious to know about the generalizability of this finding. You're absolutely right, Stephen. What

parent sends their kid to violin lessons because you're going to be a violinist. Oh, I know a couple. But the vast majority, I hope, they're sending them for this like meta stuff. You're going to learn how to do hard things. You're going to learn how to win and to lose. So I do think this games practice, which was an alternative to the math practice, but both of them were supposed to build endurance. I think it's interesting how closely that resembles the whole extracurricular function that at least American parents do a lot of.

So those are the treatment conditions, 20 to 30 hours. It's all done on an iPad kind of tablet. They disabled features. It wasn't like these 20 to 30 hours were necessarily fun. They strenuously point out that there were no fancy animations. You couldn't surf the web. So not

particularly fun training. This reminds me, since we're talking about a paper here which argues that students from low-income backgrounds exhibit what's called cognitive fatigue more quickly, this paper feels like part of a literature that I'm sure you know quite a bit about, which is the literature arguing that poverty itself is just exhausting. There's a paper by Sendhil Malanathan, Elder Shafir, and a couple other authors that

The title of that paper is Poverty Impedes Cognitive Function. The idea that being poor is essentially exhausting. There's so much effort and cognitive effort into just getting by. It really was such an important finding.

that being poor is not only an emotional burden, it's a cognitive burden. And the way they tested this was they tested how farmers did in different times of weather, like after a drought. So if I see that a farmer is doing worse on cognitive function tasks when they're

things are bad in the climate, no harvest, the weather is terrible, but not because of anything you did or didn't do, then I have evidence that there is a cognitive load to poverty. And that's what they found. But importantly, it opened up this possibility that maybe one reason why kids in school from disadvantaged backgrounds aren't doing well is maybe that there's a cognitive load

load to what they have to deal with. They're thinking about a million problems that privileged kids may not be. But it's very complicated because just knowing that alone, if you're like, wait, if self-control is like a muscle and these kids are lifting around cognitive barbells, that would lead you to the conclusion that poor kids should have stronger muscles because of all the things that they've had to deal with.

That's a great point, but you also just noted how complicated it is. And one complication that this new paper that we're talking about points out is that some schools are much better at essentially training students to have more cognitive endurance and no surprise at all.

schools where higher income students go to tend to be the schools that are much better at teaching that. And let me say something that I think will help. We're very attracted to metaphors like cognitive endurance is like a muscle. You strengthen it with use and repetition. But in the short term, when you're doing that strength training, maybe in that

Yeah.

Yeah.

It's like a signal. And in this case, fatigue generally signals, hey, you've just done something that took a lot of intention and a lot of energy. Maybe you should do something else because the return on investment in something else might be more beneficial. It's so interesting. It reminds me of something that happened just yesterday. I was playing golf up at my club and it was Championship Sunday. It was the finals of all these brackets.

And the last group to come in were these two fellows. I didn't know who'd won. And one of them pulled up in his golf cart. And I know this guy fairly well. He's a lovely older gentleman, very good golfer, very polite, very generous. He's never thinking of himself first, I guess I would say. But yesterday he pulled up in the golf cart. But I said, hey, Rick, how'd you do?

And he just did a thumbs up, no word, meaning he won his match. He's a champion in his bracket. And then it was time to come over to take pictures. Every winner got to stand there with a trophy and take a picture of

And someone said something to Rick, and he's also very pleasant, just a nice smile always. In this case, no smile at all. And when someone said something to him, he said, I'm sorry, I'm just so out of it. In my match, I was down five after 10 holes, which is essentially an insurmountable deficit. And yet he came back to win. He said,

I used every single ounce of my physical and mental energy and I have nothing left. And it was so amazing to see this person have a totally different character in the moment. He was like a zombie. He seems spent. Makes you believe in that metaphor, doesn't it? And you put it perfectly. It wasn't just the physical. It was the mental. The stress of coming back.

from that deficit had just used up everything he had. And so you realize, plainly, there are limits to this. As you said, it's more complicated than a muscle. But if it's more complicated than a muscle, how would you describe it, especially for those of us who want to use it for something outside of school? Is it more like a skill?

Is it more of a preference? Like I choose to have cognitive endurance. How do you begin to think about the complication of what cognitive endurance is and how it can therefore be boosted?

So here's what I think is going on with, I'm sorry, who was this distinguished golfer? His name is Rick. And I'll give his last name because I was very proud of him. And he's a good guy. His name is Rick Powers. Oh, great name. Rick Powers. Maybe his middle name is Cognitive. Yes, maybe it is. So Rick, I know, was experiencing mental fatigue. I mean, he said so. What was going on there? I'm saying it's

there was a signal that his brain was saying like, hey, Rick, you know what? You're in a position of having just expended tons of energy and attention toward the same goddamn thing. And you might want to

think about doing something else or potentially, I mean, look, I don't know how hard he was concentrating. I do think at outer bound limits, there could be something where your mind really can't sustain activity anymore. But what I want to say about the signal is it goes off well before it's anywhere close to its limit. Let me tell you about another person who

And they're not a golfer and they're not a guy. There was a graduate student, I believe, at Columbia University. I don't remember her first name, but her last name was Arai, A-R-A-I. And she did for her Ph.D. this dissertation on cognitive endurance and cognitive fatigue.

And back in the day, this is like 1912 that it was published. You often did psychology just to yourself. You're like, I wonder what it's like to do this. I guess I'll do it. And so what she did was she trained herself to do four digit by four digit mental math multiplication. So imagine, Stephen, 1872 times 7,641 times.

solve that problem in your head without using paper and pencil. All right. 14,303,952. You're a genius. By the way, Arai did this well before Google. What she was doing is she was just setting herself up to do incredibly mentally effortful activity.

She trained herself up to a level of competence where she was getting things right and not getting any better. And then what she did, Stephen, is she sat in a room and she did these math problems in her head, one after the other, only with occasional breaks to go to the bathroom or eat a sandwich. And then she would go right back to it.

She plotted her accuracy on a graph. Like, how did she do? Hour one, hour two, hour three. And she did this for hours in a row on consecutive days. And what did she find? Did she get better? Did she stay flat or did she go down? I will give you this clue. Each of the days really pretty much resembled each other. So you could just take a snapshot of one of those. So what did the graph look like?

I would imagine it's a slightly unequal parabola, meaning I would think that she probably peaked before the midpoint and then kind of held steady and then began to fall toward the end. That's what I would guess. She...

started off strong and just got worse. There was like a little uptick. I think it was after lunch. I mean, isn't the moral of almost every story have a sandwich? Yes. I really think that many of the world's problems would be solved by turkey and cheese.

Vladimir Putin, have a sandwich. But anyway, the idea of Arai's thesis was that there was a kind of strength that was depleted. And by the way, the reason why your parabola thing did not happen is that, remember, she had pre-trained for this. She had gotten to the best that she could get at mental arithmetic. And so there wasn't any learning. She was just performing. Now, her conclusion that fatigue...

has a lot of features of physical fatigue, I think is the wrong conclusion because really my interpretation is that what happened is that she was getting this signal. She was experiencing this fatigue that was in so many words, the mind and the brain saying, you're spending all of your attention doing this thing. Are you sure you want to keep doing it? By hour 12, she felt exhausted, but I don't think she was exhausted.

I don't quite understand what you're saying about the signal when you're saying,

Yourself, your mind, your cognition is sending you a signal that you feel depleted, but in fact, you're probably not as depleted as you think. What would the purpose of that be? Is it about reserving some energy, whether cognitive or physical, in case of emergency that there is the saber tooth tiger? Is it an alarm to tell you, you know, the house is not on fire yet, but it's getting really warm? Is that the idea?

I think that so many, maybe all of the feelings that we have, hunger, pain, thirst, sleepiness, anger, envy, elation, I think all of them are signals. They're all like fire alarms of one kind or the other. And they are trying to do it in advance of catastrophe. For example, when you have hunger, you're not about to keel over, but it would probably be good that you get to have a sandwich right now, right? Again, sandwich theory of everything. Yeah.

And I think fatigue is a signal, not necessarily that your brain is about to explode, but I think the signal is you've spent so much time and attention on the thing that you're doing, there might be something else that you would more profitably do. We talked about this briefly. I think it was a while ago. So maybe 20 years ago, there was this theory that came out in psychology that was enormously popular. It was proposed by a psychologist named Roy Baumeister.

It's called the ego depletion model of self-control. Ego depletion, meaning that there's something inside us, our mental capacity, that is depleted with use. And the most popular metaphor that the authors, led by Roy Baumeister, used was that the ego depletion of self-control is like a muscle getting tired with use,

but over time that could get strengthened also. So the idea that you could really wear out your self-control by using it up on a really hard day of mental arithmetic or a four or five hour session taking the SAT was very popular and led to these experiments where the actual thing that was depleted was being investigated. Like what is...

And the obvious target was glucose, that the brain runs on sugar. It needs energy to run. Maybe what happens when we try things that are mentally hard is that what we're really depleting is blood sugar in the brain.

And so there were these studies done. You know, what happens when people do cognitively effortful stuff and we see their performance declining, but then we give them some lemonade? What was found was that you do get improvements. It does seem to restore the ego. It seems to restore our self-control. Imagine Arai eating that sandwich. Maybe what happened after she ate that sandwich is that her brain got some glucose. Ta-da!

and she's restored. But later, neuroscientists pointed out that that can't really be that we drink some lemonade, all of a sudden the brain is recharged. The brain has all this machinery that keeps its level of glucose quite constant. It does not turn out to be anything like a plausible explanation for changes in our performance. It must be changes in motivation and attention and not like, oh my God, your brain is literally like a car without gas.

Still to come on No Stupid Questions, Stephen and Angela discuss why certain activities produce cognitive fatigue and others don't. My classes are three hours long. I have more energy at the end.

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Now, back to Stephen and Angela's conversation about cognitive endurance. I actually wrote this paper. It's a paper that I wrote with a few collaborators, and it was asking the question about whether ego depletion, the idea that self-control relies on a strength that can get reduced with use, is it really true? We said that that signal can very often be telling you about opportunity cost. And psychologists don't talk about opportunity costs very much, do they? Absolutely.

I know. I felt like if behavioral economics is importing psychology into economics, this was... Let's bring a little econ into psych. Yeah, I agree. So let me ask you to define opportunity cost because you do hang out with economists. How would you, in lay terms, explain what I think is an extremely powerful idea? Here's a way I would explain it to someone. I would say...

that every dollar or hour or brain cell that you spend on something means that it cannot be spent on something else, at least simultaneously and sometimes never.

And also, you'll notice in my definition, I include a brain cell in there. Now, I don't mean your brain cell if you use it that it's actually gone for good. But if I spend my time thinking about X, then I can't spend my time thinking about Y. And moreover, if I spend a lot of time thinking about X, which may be some guilty pleasure, maybe I love to watch rom-coms.

Not only am I unable to spend my time in that moment differently, but I may develop habits that lead me to not be able to spend my time more profitably later on. And so that's how I think about opportunity cost. It's basically a really nice theory to act as, to use the language of my friend Angela Duckworth, a signal that

to constantly be inspecting what you were spending your money and time and brain cells on. And that's where I think that psychology could incorporate that more robustly, because I think it's a very powerful behavioral concept beyond the financial realm.

And when you talk about opportunity costs, you're exactly speaking to what we propose as what that signal is telling you. One of the co-authors on this paper with us is Joe Cable. He's a neuroscientist. And when we were talking about this, he thought very hard about what it is that the brain does that produces an experience of fatigue. And what are the things that the brain does that

Yeah.

Yeah. So when we got together, this is the golden era of the ego depletion theory. Everybody was talking about it. I think it was around the time that Barack Obama was saying he doesn't want to make too many decisions that are trivial because he's got to put his mind on important things. The popular inference was that you don't want to tire out your decision-making muscle. You want to save it. Yeah.

And there's some interesting empirical evidence that people seem to wear down and make less good decisions in the real world. Baseball umpires, judges. The question is why that happens. And is it because you have a physical thing in you that gets depleted? Is the brain really a muscle? Like muscles actually get tired. I mean, there are things that happen in muscles that make it impossible to contract them over time. But

But the brain is literally a muscle, right? It's not literally a muscle. Is the brain not a muscle? Do all the things that happen in your bicep not also happen in your brain? Isn't there all the exchange of all those chemicals and blah, blah, blah? It's like a chemical computer. There's a lot of electricity that's running around, but it's running around with these ions that are charged as opposed to on wires.

So the brain has certain things in common with muscles because muscles also have a lot of this electrochemical stuff that's going on. But muscles and brains are not the same. So it's not a muscle, but it has some of the components of a muscle.

And because some of those components are blood vessels and nerves and neurons and all those things, wouldn't it make perfect sense that there's depletion in the brain just like there is in a bicep? Well, let's talk about actually what would be depleted. If the brain were being depleted of something, what would it be depleted of? It would be depleted of an ability to function further without a sandwich. Right.

Well, the glucose model of this kind of self-control strength that we have has been pretty affirmatively denied. So the thing that happens when you have a sandwich and when you have a drink of lemonade, actually, that's been shown also, if you give somebody a small gift, like they're doing something really mentally taxing and their performance is going down, down, down, but then you just give them a gift. Right.

or praise, it goes up again. So I think what happens again, it's all about signals. It's about mental representations. How's this going? Is this worth it? And I think what happens when you get really tired is that you're getting a signal that like, hey, are you sure you want to spend all of your attention on this one thing? And are you sure it wouldn't be better to move to something else? What's the marginal return on investment of looking over there instead of where you're looking here? So Angela, I have to say,

This is one of the most fascinating conversations I've ever had with you. Thank you. And yet I feel we have so much more to say because we literally haven't gotten to the meat of the paper itself. We didn't even get to their findings. Can I say, though, I don't regret it for a second because I feel like you've taught me and all of us so much about.

forget about even cognitive endurance or cognitive depletion, just cognition and how it intersects with our decision-making and our physiology and our mental state and so on. So I am going to propose something bold and perhaps stupid. Wait, can I guess? Yeah. Part one and part two? Part one and part two. We've never done that. And maybe it's a terrible mistake. I would ask our listeners, let us know if you hate this idea. It's obviously just coming up at the spur of the moment, but

I would hate to take everything that we've talked about today and whittle it down to eight minutes to make room to talk further about this topic. This is like a cliffhanger. This is like who shot J.R. It is so much like who shot J.R. So I think that for now we should stop.

Really, there's one big reason why I feel we need to stop now, which is I think that you have so earned yourself a sandwich. And I don't think the sound of you eating while talking is good for our misophonia friends. And so I think it's time to put down the microphone, pick up a sandwich, and we'll return with the actual findings of the paper. Can you buy into that, Angela? Yeah, let's continue this conversation. There's too much to say.

But let me not buy into the fact that I need a sandwich. Do you know, Stephen, that right now I don't feel fatigued. I feel energized. I'm like, let's go. So that tells you the signal saying something. This is something Steve Leavitt and I have talked about a lot before because he is a classroom professor, as are you. I used to teach some, but we both have a lot of experience giving talks and also being present for other people giving talks.

You would think, I would think at least, if you ask the median person, what's more exhausting, giving a 60-minute talk in front of a few thousand people or sitting in an audience with a few thousand people hearing somebody give a talk? I would think most people would say it's much more exhausting giving the talk. Levitt and I have come to the conclusion there's nothing more exhausting than having to watch someone else's talk because when you're giving the talk,

Your brain is just firing to both of us, at least. It's incredibly energizing. Yes, you're a little bit spent afterwards. Maybe physically, but overall, you can be like just jacked. Like, where's the next eight talks I get to give? Yeah. So I'm curious, what are your feelings on acting?

active exertion of energy, cognitive, physical, et cetera, versus watching other people do the same. I completely feel how you and Levitt feel about giving a talk. When I give a talk, it could be three hours, which is usually how I lecture. My classes are three hours long. I have more energy at the end than I did before. I mean, again, I can feel sometimes my back or my knees or

There's a physical element, but I feel mentally more energized. And I think if you can, for the whole day today, notice your feelings and say, every time I feel anything, I feel tired, I feel sleepy, I feel angry, I feel proud. Those are signals. Sometimes the signals are accurate, sometimes they're not. But I think the feeling of fatigue is the signal that

Are you sure you really want to be doing this? And when you sit in a lecture for 60 minutes, I mean, maybe you're lucky enough to be sitting in Steve Levitt's lecture. Maybe you too feel energized afterwards. But I think very often we sit in lectures for 60 minutes and we're like, oh, my gosh, I don't want to be here. This isn't interesting to me. What am I going to make for lunch? Maybe I'll have a sandwich. These are the feelings that are telling you that maybe you should be doing something else. And that often is the feeling of fatigue. Right.

boredom is incredibly tiring. I'm sorry, I can't let you go. There are two things I need to say before we end part one. P-P-P-S. Number one, I think to the litany of toast language, cheers language, raise a glass every time we say Marty Seligman or Danny Kahneman. I think sandwich has just made its way into that lexicon.

Number two, you said something a moment ago that was, I think, meant to be comforting, but was instead deeply disturbing. You said all of these things, you even included pride. All of these feelings that we have are signals. And then you said sometimes they're accurate, sometimes they're not. What the heck are we supposed to do with that? How are you supposed to know when they're not accurate?

Well, I think what we're all trying to do is become more metacognitive. And what the hell do I mean by that? Yeah, what the hell do you mean by that? Well, I guess Zuckerberg has taken the word meta and wants to make it what he wants. But we use the word meta and metacognition in psychology. And what the idea is, is that only human beings, not squirrels, not dogs, not horses, and not even chimpanzees, have the ability to think about their own thinking, to have a layer of

of cognition, which takes yourself as the object of interest. In other words, I can feel anxiety, but not only can I feel anxiety, I can say to myself, huh, you know what?

I just felt a little anxious just then. What does it mean? What is that signal? Do I think the signal is accurate or do I think it's not accurate? And I truly believe that the seed of all personal development and growth is becoming more metacognitively sophisticated. And it's not just me, by the way. Developmental psychologists like Phil Zalazzo and others have suggested that is what maturity is, becoming increasingly able to see yourself in perspective and

And you're saying my pet squirrel could not do that. Right. What about Rocky the flying squirrel? He was pretty damn sharp. Rocky and Bullwinkle. I hated that show so much. You know why? Because that was a squirrel with metacognition and you were a little bit jealous. Yes. Maybe that's what was going on. I'll take that into consideration. No Stupid Questions is produced by me, Rebecca Lee Douglas. And now here's a fact check of today's conversation.

In the first half of the show, Angela tells the story of a Columbia graduate student named Arai who researched cognitive fatigue by performing mental multiplication. The researcher she was thinking of is Japanese psychologist Tsuruko Haraguchi, born as Tsuru Arai in Japan in 1886. Haraguchi was the first Japanese woman to receive a PhD in any subject.

In addition to testing her mental endurance through complex multiplication problems, she also translated German words into their English equivalents and English sentences into Japanese. Her doctoral thesis on mental fatigue notes that she did stop her research for meals, but it does not indicate that those meals necessarily involved sandwiches. She died of tuberculosis in 1915 at the age of 29.

Later, Stephen wonders if the brain is a literal muscle. Angela was correct in saying that it's not. It's an organ. And at 60% fat, it's actually the fattiest organ in the body. While it does have muscle-like qualities, the brain contains no literal muscle except for the tissue between arteries that carry blood to the brain.

Finally, Stephen references a paper called Poverty Impedes Cognitive Function and mispronounces the name of one of the authors. The researcher's name, pronounced Sendhil Mulinathan, is a professor of computation and behavioral science at the University of Chicago Booth School of Business. That's it for the fact check.

Coming up next week on No Stupid Questions, Stephen and Angela actually get to some answers about whether cognitive exercises can help your mind feel stronger longer. I don't recommend personally putting kids on iPads to do 20 or 30 hours of training. I think you can do better than that. That's next week on No Stupid Questions.

No Stupid Questions is part of the Freakonomics Radio Network, which also includes Freakonomics Radio, People I Mostly Admire, and Freakonomics MD. All our shows are produced by Stitcher and Renbud Radio. This episode was mixed by Eleanor Osborne. We had help this week from Jacob Clemente. Our

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Oh, my God, Stephen. I have so many things to say. Don't say any more, though. Save it. The Freakonomics Radio Network. The hidden side of everything. Stitcher. Hey there. Stephen Dubner from Freakonomics Radio here to tell you the national sales event is on at your Toyota dealer. Now is the perfect time to get a great deal on a dependable new SUV like an Adventure Ready RAV4.

Available with all-wheel drive, your new RAV4 is built for performance on any terrain. Or check out a stylish and comfortable Highlander with seating for up to eight passengers. Available with a panoramic moonroof, you can sit back and enjoy the wide-open views with the whole family. Check out more national sales event deals when you visit buyatoyota.com. Toyota, let's go places.

Every sandwich has bread. Every burger has a bun. But these warm, golden, smooth steamed buns? These are special. Reserved for the very best. The Filet-O-Fish. And you. You can have them too. For a limited time, the classic Filet-O-Fish you love is joining your McDonald's favorites on the two-for-$3.99 menu. Limited time only. Price and participation may vary. Cannot be combined with any other offer. Single item at regular price. Ba-da-ba-ba-ba.

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