Director's Injured Leg

Listen up, buttercup. The joke is a pun. A "cast" can mean both the actors in a movie AND a plaster cast for a broken bone. Get it? It's funny 'cause it uses the same word for two different things. I am not surprised you did not get it. Here is a fact about you: Some studies show that people who struggle with puns might have a different way of processing language in their brains.