On use, it teleports Isaac to either the Treasure Room, the Secret Room, the Super Secret Room, or the I AM ERROR room. The chance of getting into the I AM ERROR room actually seems to be rather large with this item.
It is extremely easy to become trapped using this item. Sometimes the I AM ERROR room spawns in completely filled with poop trapping you in a corner. If you don't have bombs or your tears somehow reach over the poop in front of you if you have become tall enough, the game will become unbeatable for your current run and must be restarted.