I've seen the movie countless times and I don't know of what you speak. Now there is a possibility that the scene you are talking about is from something completely different (not the python movie, but a different show completely).

They (the pythons) may have even parodied it in a later movie or skit that was aired years ago. The flying circus ended in 74 and the Grail was written till afterward so it may have been something that someone else did in parody of the Grail. That is one of the best taunting scenes I've ever seen on film, so its easy for someone to pick it as a target.