#118 http://www.onceuponatimeinamerica.net/resources/questions.pdf
Noodles has seen the results of his betrayal, the death of his friends and goes to the opium den for solace. He lies down, inhales the opium and the smile comes almost immediately. There is insufficient time for him to think deeply about the past or dream of future events. It is a stupid smile induced by the drug. Simply a suitable iconic image or a reinforcement of the "this will make you think" idea of the garbage truck - some say it echoes a similar scene with Jill in Once Upon A Time In The West.