Here's a fun one to wrap your brain around.
I have a certain female friend, we'll call her jenn for the purposes of this story. A few years ago when I was in college living with several roommates in an apartment, my one roommate had some... plantlife growing in his closet. Because they were in the closet, he needed to set up some lamps that were on an automatic timer.
So one day Jenn is visiting us, and she finds the plants b/c the lamps were on at the time and she though he had left his closet light on. Now she had never seen a closet project like this before, and she was asking us about the lamps, specifically what would happen if he forgot to turn them off... conversation is as follows:
Me : “He doesn't have to remember to turn them off, they have a 24 hour timer, they run for however long he tells them to then shut off, then turn on the next day at the appointed time.”
Jenn : “oh”
At this point Jenn gets a really puzzled look on her face. Then she says it, the dumbest thing I've ever heard:
Jenn : “If there are an even number of hours in a day, and an odd number of days in the week, how does that timer stay accurate?”
*jaw drops, brain tumor develops, I pass out for an hour*
To this day I still can't figure out what chain of thoughts led to that question/conclusion.