Now that I've driven everyone crazy, I just realized that I made a mistake with my first clue
The reference to dropping something was in the novel, but not really indicated in the film. It happened with the toll collector, when Sonny was shot on the causeway. Sonny, who is in a hurry, hands the toll collector some money, and then watches with annoyance as he "drops" it, and bends down (ducks) to pick it up. I can't supply the exact quote at the moment, because I don't keep a copy of the novel in my office (but probably should).

Sorry about that. I'll go to my corner with my dunce cap on, now...