Deck of Cards and Pony

Okay, listen up, buttercup. The "joke" is playin' on words. See, a deck of cards has jokers in it. And a "joker" is also someone who jokes around. Now, a pony is a small horse, right? So the punchline is that both a deck of cards and a miniature pony are "jokers." Get it? Probably not, you wouldn't know funny if it bit you on your saggy can.