Quib.ly has five things you may not have known about Minecraft, including Killer Bunnies:

There is however, one deadly exception. Whenever a rabbit is spawned by the game there is a small chance that what will appear is not the twitchy-nosed ball of cuteness you might expect, but a terrifying killer rabbit with glowing red eyes – a tribute to the Killer Rabbit of Caerbannog from Monty Python and the Holy Grail.

/via Fire Tech Camp