It's not funny. It's terrifying.

Whenever I see a movie, tv show, or ad where they have someone falling on a treadmill as a joke, I always wonder if the person who came up with the idea had even fallen on one before.  If they had, I don't think they'd have made the joke.  I think they'd be thinking about how long it took the skin that was sanded off to grow back, and the utter terror they experienced when it happened.