conundrum

noun (pl.conundrums) 

• a confusing and difficult problem or question: one of the most difficult conundrums for the experts.
• a question asked for amusement, typically one with a pun in its answer; a riddle.

Have you ever wondered if water really goes down the plughole the other way on the other side of the equator?

Have a look at this ... on Youtube

Perhaps it's to do with Coriolis.