A lot of kids have this game, and also spend a lot of money on it. There is a high change kids are going to try this at home at some point, as they are very manupelative, espacially when they have bad parenting and a pistol laying around.

Thus it has to be less bloody and all. Replacing the bullet with a party popper like explosion, let the spy have a scared face, and possibly when co-operating with valve, making him say: Lucky I didn't use a bullet. I'm alive! I'm alive. or You didn't think I was that stupid, did you!, then after he said it making him fall to his knees, landing face down as he scared himself to dead.