What is cat that ate the canary?

"Cat that ate the canary" is a phrase that is used to describe a certain behavior of a person or animal who appears to be smug, self-satisfied, or pleased with themselves after having succeeded in deceiving or fooling someone. This phrase originated from the idea that a cat might have a satisfied expression on its face after having caught and eaten a canary, as if it had pulled off a successful trick.

In certain situations, a cat that ate a canary can also mean that someone is bragging or boasting about something they have done that may not be entirely ethical or legal. It can also indicate a sign of guilt or nervousness after getting caught in a wrongdoing.

Overall, the term "cat that ate the canary" is a metaphorical expression that refers to a person or animal's smug or sneaky behavior after successfully getting away with something they shouldn't have.