"That's the most foul, cruel and bad-tempered rodent you ever set eyes on!"
Rabbit of Caerbannog, and the bones of full fifty men strewn about its lair
The Killer Rabbit of Caerbannog is a monster in the film Monty Python and the Holy Grail.
The rabbit guards the entrance of cave where the location of the grail is written on the wall, surrounded by the bones of its victims. When Tim the Enchanter leads King Arthur's knights to the cave, they at first mock him for being afraid of a harmless animal, and Arthur order Sir Bors to behead the bunny. The rabbit leaps at Bors with razor-sharp teeth and beheads him instead, to the other knights' shock and Tim's satisfaction.
The Killer Rabbit attacks.
The rest of the knights charge the entrance but have to retreat after more casualties. Determined to enter the cave, Arthur requests the Holy Hand Grenade of Antioch and uses it to blast the rabbit out of their way.
The rabbit also appears in Spamalot, where it is revealed in-story to be a puppet rather than a live animal.