A riddle is a puzzling question or statement designed to make you think hard before you discover its clever answer. The Sphinx in Greek mythology asked travelers, “What walks on four legs in the morning, two legs at noon, and three legs in the evening?” The answer: a human being, who crawls as a baby, walks upright as an adult, and uses a cane in old age.

Good riddles use wordplay, double meanings, or unexpected perspectives to hide their answers in plain sight. When someone asks, “What has hands but cannot clap?” they're using the double meaning of “hands” (the parts of your body and the parts of a clock). The answer: a clock.

Riddles appear throughout history and across cultures. Medieval knights encountered them in legends, while children today still puzzle over questions like “What gets wetter the more it dries?” (a towel). The Hobbit features a famous riddling contest between Bilbo Baggins and Gollum.

The word can also mean a mysterious situation that's hard to explain or understand. Scientists working to solve the riddle of how birds navigate thousands of miles during migration, or detectives trying to solve the riddle of a mysterious disappearance, face puzzles without clear answers.

As a verb, riddle can mean to fill something with holes or problems. When something is riddled with holes or problems, it's full of them, like Swiss cheese riddled with holes or an old theory riddled with mistakes.