Great subtle moments in movies

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The Manchurian Candidate, the scene where Sinatra meets Janet Leigh on the train. He is a complete mess, a nervous wreck, and they have this exceedingly strange dialog. No woman would be attracted to this man and yet she is, or is she an agent giving him instructions in code, or just what is going on in this scene? It's subtle because if you aren't paying attention it seems normal, I thought nothing of it the first few times I saw the movie besides its illustration of Sinatra's desperate state, but the more you watch it and think about it the weirder it gets.