One of my definite favorites from the 3 GF movies was in Godfather Pt II, right before Fredo is about to be shot in the boat, when Connie calls Anthony to the car.

When Fredo is leaning out of the boat, telling Anthony that he'll use the secret trick to catch the fish, if you look in the background at Al Neri's face, he's got this really broad grin on his face. I always was a little bit shocked by it considering what he's about to do to poor Fredo. Definetly not something you're supposed to notice, but I always did.