To the left of the 'WARNING" door in the starting area of SNN there is a hung man.

If you stand by the window near the ARISAKA, bounce 1 or 2 grenades off the ground near the maggots so that they end up by the lantern at the feet of the Hung Man. When it works, the Hung Man's feet will get caught on the wall behind him. When this happens, he will stay like that for about 5 seconds and then drop to the floor, the rope extending to let him reach. He may end up on either side of the 'WARNING' Room wall. Once on the floor, he will do some small 'jumps' (usually 2 at a time) about a game foot off of the floor. If you touch him when he is 'jumping', you will die.

I have been told that it may reset a multiplayer game when a player dies from it, but in a 1 player game, it just kills you.

Note that it otherwise does not affect game play. Despite rumors, it has no effect on zombies at all and does not automatically reset the game. A few days ago I accidentally knocked him down on level 9 and by level 119 he had made his way out onto the 'balcony' by the 'Slide and Ride' but never interrupted my game at all.