Androcles' Lion: If you feed the giant rat a sandwich, it will stop attacking you � and the mere existence of a non-lethal option in the first place means the rat is, by a large stretch, the friendliest creature in the game.It's also useless against most monsters, as they'll kill Tabby before she can kill them (the Zombie Cat being the only exception Tabby can kill it with the axe if she can get the jump on it.) You can also use it to murder your family.
It can be used to break certain objects, but will break itself once used three times. There are also two secret diary entries that can only be obtained past this point. This lets you look for more things you might have missed. The monster in the fridge will eventually eat her if she's left like this.