The startled painter twice leaves a streak of paint on the wall. First, when Gunn enters the room. Second, when Jacoby enters the room. Each time, the streak in the closeup shot appears different from the streak in the distant shot.
When Edie calls Gunn, he is cleaning the barrel of his revolver. He's running the brush through the barrel front to back. Any gun owner knows the correct way is to open the chamber, and run the cleaning cloth (or brush) through the barrel from back to front. NB: The cleaning of a revolver barrel needs to be done from the muzzle (as shown) with a cleaning rod. The cylinder, when opened, can be cleaned from the back.