| In Monty Python-dialect French, this phrase means literally "Get the cow!" as an imperative. It is heard in the magnificent work The Holy Grail when the Taunting French Knight snaps this order to his fellow knnnnigits within the castle. Moments later, with a resounding mooooooooooooOOOOOOO! a large cow (it appears to be a Holstein) flies up over the castle walls, to the consternation of Arthur and his men. It was fired, no doubt, from a cattlepult, probably one of the best they-didn't-actually-say-it jokes ever filmed.
Note: Spuunbenda has informed me that it was a trebuchet, not a cattle-er, catapult. My mistake, and thanks for the note S! | 
