Setting a spider den aflame and trying to pick up the spiders after they fall asleep will result in a server crash. The spiders you pick up don't show up in the inventory but webber says that his inventory is already full. After this you are unable to pick up items and after 10 seconds or so the server will crash. Updated, If you use a pan fluit to make the spiders sleep they also crash the game when picked up. To crash the server you need to leave it then everyone else crashes.