Rusty Metal Disease

Hey, you dummy! So, you know how when you get a cut from something dirty and rusty, you can get tetanus? Well, this joke is playing on that. It sets up a really gross and absurd scenario – shoving dirty, rusty metal... *there* – to make you cringe. Then, the punchline is just the obvious medical answer, "Tetanus." It's funny because the setup is so over-the-top disgusting, but the answer is totally normal for a rusty metal injury. You probably didn't even think about the medical accuracy, did you?