Falling off the roof
The scene that made me laugh the hardest is when Sellers was up on the roof, and the way he was scrambling, slipping and sliding and trying his best not to fall off the roof. That type of physical slapstick is by far the best I've ever seen (Charlie Chaplin notwithstanding). His dexterity in portraying a clumsy guy is nothing short of phenomenal. (I mean, to say that he surpasses Chaplin at his brilliant game says it all:)
Then, when he finally falls off and splashes into the swimming pool, he utters some mumbling unintelligible word that resembles baby talk, which makes this man even more endearing to watch. Does anyone know what was it that he exclaimed when he fell into the pool?