What's the connection between "Holy Grail" and "Killer Rabbit"? [closed]

This article says:

If there's a Holy Grail, there's a Killer Rabbit.

I can understand that to be "even if there's a good solution, there's a catch to it", but what does Killer Rabbit have to do with the Holy Grail?

It is a reference to a Monty Python film from 1975 called Monty Python and the Holy Grail

http://www.youtube.com/watch?v=XcxKIJTb3Hg

The Rabbit of Caerbannog can be killed by the Holy Hand Grenade of Antioch.

By way of a long addendum to mplungjan's answer...

If you are going to be interacting a lot with English-speaking people, then as a point of cultural literacy, I highly suggest getting hold of this movie and watching it through at least once. This is probably not the first reference to it you have encountered, and it almost certainly won't be the last. Your typical techie can quote large sections of this film from memory, and knowledge of it is pretty much assumed. (Plus, it's f'ing hilarious)

Other MPatHG references you may stumble across include, but are not limited to:

• Tim the Enchanter
• The Holy Hand Grenade of Antioch
• Air-speed velocity of swallows.
• Answering questions wrong resulting in being thrown in a pit (often: "Red...no Blue. Aieee!")
• Trojan Rabbit
• Sir Robin's Minstrels (occasionally the eating thereof)
• "...and then it fell into the swamp"
• "Runaway!!"
• "`Tis but a scratch!"
• Catapulting cows