Note: despite widespread misconceptions to the contrary, MontyPython's dead parrot sketch was, in fact, not that funny.
The DPS is about JohnCleese's fury with himself for being so openly tricked into buying an obviously dead parrot. All the haranguing in the onscreen sketch refers to John's previous visit.
But any humor is lame when you analyze it.
Regarding PairProgramming, the group wrote in pairs. John started the parrot sketch with some other animal, and muddled thru it without humor. Then GrahamChapman asked, "but what if it were a parrot?" and the rest is history.
Was it a slug?