My father also introduced me to this movie. It was a movie that he and his best friend loved when they were young (the other was Stalag 17 which should be on the list by the way). And we would watch this movie together every time it was on tv. The mirror gag as well as the lemonade vendor bit are comedy classics and I don't think that can be disputed. And the verbal gymnastics of some of the scenes always blow me away. "How am I gonna find out what I wanna find out if he no find out what I wanna find out".