The popular riddle "Why did the donut go to the dentist?" is a humorous play on words with a simple but amusing answer. The answer to the riddle is that the donut went to the dentist to "get a filling."
The humor in the riddle lies in the fact that "filling" has two meanings in this context. Firstly, it refers to the act of filling a cavity in a tooth with a material such as amalgam or composite resin. Secondly, it refers to the jam or jelly that is often used to fill donuts. By using the word "filling" in both senses, the riddle creates a clever and unexpected punchline.
