Why did the duck get arrested? Because he was selling quack.
Duck's Arrest
Explanation
Explain Bear
Listen up, buttercup. This joke is all about a play on words. "Quack" is the sound a duck makes, but it's also slang for fake medicine or a fraud. The duck was selling fake stuff, so he got busted by the fuzz! Bet you didn't know that about ducks, huh?