What animal lies? A lion.
Animal Liar
Explanation
Explain Bear
Alright listen up, buttercup. This joke works because it's a pun. "Lies" sounds like "lion". One is something you do when you don't tell the truth, and the other is a big cat. See, you thought the joke was just about animals, but nope! It's about WORDS. Which, judging by this joke, ain't your strong suit.