When Secrets is learning to load her gun, the cartridge shown is for an automatic pistol and is rimless. It could not be loaded into her revolver.
Secrets' gun is a single-action revolver. When she "accidentally" fires it, it is not cocked, and could not have gone off whether she pulled the trigger or not.
(at around 30 mins) When Greg Swank is trying to remember the combination, as he swallows, the lower part of the tube stuck through his head moves independently from the upper part, because it is made from two pieces.