Lauren "The Walking Dead" Cohan's joke in the latest Esquire

There's this actor, Marty, in his 50s living in L. A. who's never had his big break. One day, his agent calls him. "Marty, you're not gonna believe it.
I got you a part. It's on Broadway. It's just one line, but it's a huge play. And you're on tomorrow night."

Marty says, "This is great. What's the line?"

The agent says, "Hark! I hear the cannons roar."

Marty agrees to the part, and he's thrilled. He gets to the airport and starts saying the line out loud over and over again all the way to New York.
"Hark! I hear the cannons roar. Hark! I hear the cannons roar."

All the way to the theater he runs the line. He gets to the theater, goes backstage, waits for his cue.
He runs onstage and hears the cannon. Bang! And he screams, "What the **** was that?"