This happens to be Burt Reynolds' actual last Gunsmoke episode, even though 'Bank Baby' was his last broadcast episode, (per the production numbers in the Barabas' Book on the series). The very last scene features Quint, Doc and Festus on a Dodge sidewalk. Festus is holding a coin, which his nephew Eliab, off screen, shoots out of his fingers, (Festus has introduced a widow looking to marry someone- anyone- to Eliab to get her off of himself and Eliab has just realized what he's done.).
I'm always interested in how these scenes are done and so I watched this one over and over again in slow motion. The first thing i noticed with that both Doc and Quint react to the shot well after it would have driven the coin past them. Maybe that's normal but it looked as if they were responding to a cue rather than a shot and the timing of the sound, which would have been added afterwards was slightly off their cue. I then decided that Ken Curtis had simply let the coin drop into the palm of his hand rather than had a professional marksman shoot it out of his finger. The one thing that challenged this view is a faint trace of something going on a line in subsequent frames past the three of them. But ti seemed to have a downward trajectory, not a flat one, (Eliab had appeared earlier in the scene at street level). I wondered if the coin was a on a string . I also thought perhaps they'd imposed a ghostly image of something flying past Doc and Quint after the scene was shot, to represent the coin flying away. I just don't know.
Of course if we had a message board, we could discuss it at length but we don't so I have to put this on as a review. At least it's something to look for the next time you watch the episode.