What does "cat got your tongue" mean — and why is it funny?

informal

Meaning

A teasing question asked when someone is unexpectedly silent or has no answer ready.

Where it comes from

Uncertain, despite many colourful guesses; it became a common taunt, especially towards children, in the 1800s.

Why it is funny

The humor is the bizarre little crime it invents. To explain a silence, it accuses a passing cat of having stolen the person's tongue — a surreal idea delivered as though it were the obvious explanation.

Used in a sentence

"You were so talkative earlier. What's wrong, cat got your tongue?"