IN THE CARNIVAL of pop culture, Ken Jennings—a 74-day Jeopardy! champ—rightfully holds a revered place: America's winningest game show contestant. No one else has made more money on more shows using more brains. But he's also the nicest. And, maybe, one of the funniest—at least judging by the thousands of people who buy his books and follow his surprisingly droll Twitter feed.

Jennings' latest book, Because I Said So!: The Truth Behind the Myths, Tales, and Warnings Every Generation Passes Down to Its Kids, beautifully blends all of those qualities. It's a gentle, funny, diligently researched takedown of all the stupid, unreasoned, and unadulterated bullshit parents have been spewing at their kids for generations. Turns out, eating boogers (besides being gross) isn't so bad for you. Also, no one needs to guzzle eight glasses of water a day. And feel free to do a back float after a meal—you won't drown. (But weirdly? Your grandmother maybe isn't lying when she equates chicken soup with actual medicine.)

Jennings, due at Powell's on Thursday, January 17, took time to chat with the Mercury. (And, yes, I nearly melted when he said he remembered watching me lose—the day after I won!—on Jeopardy!)

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MERCURY: There's so much trivia in this book. But it's helpful trivia. What gave you the idea?

KEN JENNINGS: I was always a fan of quirky pop reference books. I used to have a shelf full of them when I was a kid, books like Isaac Asimov's Book of Facts. Then, when I had kids myself and started repeating these clichés to them, I realized there was no reference for this. I thought, "I could actually write this."

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Each entry seems like it's built on a nightmarishly large pile of research and citations. Was that rougher than you expected?

Most of it was coming up with the list of nags parents use. We don't think about them a lot anymore, even if we do find ourselves repeating them. It required a lot of bugging friends and asking strangers on the internet. I went on Reddit and got a couple dozen that way. Finding all the studies would have been a nightmare if you were writing the book in the '80s. But now? In the Google age? It's easy to find four people who have done studies on something.

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Which means we're all capable of saving ourselves. What surprised you when debunking?

I've been around the block. I know, for example, chewing gum doesn't stick in your stomach for years. But I was so sure the thing about eight glasses of water was right. Or the fact that "don't talk to strangers" is actually bad advice. That's the opposite of anything we expect.

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Did your parents take it personally?

They recognized that the parents in the book aren't them. It's a composite of mid-century parents from movies and TV. What's worse is my son has read it. Now we can't tell him anything. "No. It's in dad's book," he'll say. "It's fine." Of course, when you tell your kids something, accuracy is not the only goal. Sometimes it's to stop your kids from being annoying.

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Anything surprise you when it turned out to be correct? 

The chicken soup for colds, that struck me as the old-timiest, most old-world superstitious, nice well-meaning Jewish mom, how-can-that-be-true sort of thing. But a couple of studies show it's better than other liquids. Is it just a coincidence? Is it just an accident that it turned out to be true?

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This seems like an awful book to have to update. So much shifting science!

I'd hoped more answers were straight up or down. But I had to do my own meta analysis of all the data. The book is full of judgment calls.

There are things that are not in the book because I was worried about the consensus changing tomorrow. The effect of videogames on a kid's temperament? The dangers of cell phones? My editor was concerned about phthalates and plastics. There's all this stuff that could actually change tomorrow. Maybe I could pay an intern to do it.

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Were you funny before being on TV? Or did smiling in front of cameras so many nights in a row help you hone your craft?

I don't think I've changed that much. You know, things like Spy magazine started coming out when I was a teenager. I was the exact perfect age. It's just that Jeopardy! doesn't give you a chance to be funny. The contestant who tries to make jokes looks like a tool. You know this. People might wonder: Does this guy just tweet trivia questions? Or why does this guy still exist? Twitter is a great format for telling jokes, and that's what I've been using it for.

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Could Watson write a better advice book? [Jennings lost on Jeopardy! last year to a creepy supercomputer named Watson.]

Would he be raising little baby graphing calculators? I was reading about someone using Watson-like technology to generate if not books, at least blog posts. Since people don't want to hire writers. As a writer, that would terrify me. I would hope Watson would not replace Don DeLillo or Philip Roth.