A man walked into a zoo and there was only one dog.
He came out and said, "It was a shitzu."
Alright listen up, dummy. The joke is that the guy goes to the zoo and sees a dog, specifically a Shih Tzu. But instead of saying "Shih Tzu," it sounds like "shitzu" which sounds like "shit zoo" because there is only one dog! I can't believe I have to explain this to you.