Zap Em!

For those who haven't seen it, Fear Factor challenges 6 contestants to perform stunts to win a cash prize. Typical challenges include eating bugs, jumping across moving trucks, etc. A good idea to challenge them with something really scary would be to pretend to zap em with a defibrillator. Using them on someone who's heart is beating usually stops it, which is why they yell clear. Tell the contestants they are going to stop their heart, and then start it again <inspired by the move Flatliners>. But to avoid the pesky problem of killing them, have the paddles simply vibrate or put out a low voltage (like those video game electric chairs). See how many of them would go through with it not knowing that it was a joke.