classicmovietrivia:

 The legendary kiss between Ingrid Bergman and Cary Grant in Notorious had to be on and off during the entire two and a half minutes it lasted. This was because, at the time the Hayes Code stated that an onscreen kiss could last no more than three seconds. So the two and a half minute kiss had to be stopped every three seconds to dodge the rule. Ingrid Bergman would remark how akward it was to nuzzle each other with the camera trailing behind them, but Alfred Hitchcock assured her it would look right on screen.