There are two underground passageways with manholes. You must pick one to go through. One manhole is circular and the other is a square. Which do you chose?

Question

Quizplus · Accepted Answer

The manhole with the circular cover. For safety's sake, you pick the circular manhole cover, because this cover cannot fall through its hole. Square manhole covers could fall through diagonally killing you. Tsk tsk tsk.
Key Takeaway: This is a classic brainteaser and we hate it. It doesn't really prove anything, but 3 out of 5 people who worked on this module had it in interviews, so we included it.
Editor's Note: I had a co-worker who always gave this question to undergrads. Very few of them got it, but he judged them more on how they handled the question more than whether they got it.

There Are Two Underground Passageways with Manholes