You know the Wason selection task. You know all about Linda the bank teller and the conjunction fallacy. You're smart. You'd never fall for those things now! You know it's not more likely that Linda is a bank teller who is active in the feminist movement than that Linda is a bank teller. You know to flip the Wason card that would break the rule rather than the one that would confirm it. Yes, of course!
Here's one I learned in junior high school, which I've never seen studied. I don't know the original source. (If you do, let me know!) Maybe it will be fresh to you. Over the years, when I've presented it orally, I've found that even people with PhDs in philosophy often struggle, though really it's very simple.
A man is looking at a picture. He says, "Brothers and sons, I have none, but this person's father is my father's son." Question: Who is in the picture?
If you think you know the answer, write it down. I don't want any squirreling around about what you had really been thinking!
After you've written down your guess, click through to this post on my Underblog for the answer and discussion.
[image adapted from here]