When is this riddle not a riddle? When it's a trope.

A riddle is a word puzzle with a logical but nonintuitive solution and which is typically coded through the use of Double Entendre, Double Meaning, Multiple Reference Pun, unconventional descriptions of natural phenomena, and an otherwise hidden but discernible meaning.

Riddles are primarily employed as a mental exercise or challenge that forces the listener to use their intuition, outside the box thinking, logical reasoning, and memory to find the hidden solution behind the phrasing and context given.