Have you ever sat down to watch a movie you've seen before and noticed something that never caught your eye on the first viewing? Of course you have, because there's almost always too much going on within the frames of a movie to start taking notes about its subtler moments on first viewing. That's what makes the process of re-watching a motion picture an incredibly exciting one - you get to find things that evaded you now you can focus elsewhere.
With most movies, this process proves itself to be a rewarding one. With others, it's heaven. Yes, some movies have been purposely built with the intention that you spend a small portion of your existence studying every frame in immense detail, because every filmmaker knows - as cinephiles themselves - that movie-goers appreciate films that are dense, jammed with subtle nods to other movies, and inclusive of a few hilarious (and subtle) jokes, too.
In the cases of the little-known jokes that I've assembled for inclusion on this list, you were probably too distracted at the time to notice that they were even happening. And with a good number of these, it might also have helped to have been a bit of a genius.