Continuity mistake: When Mugsy takes Bugs into the other room, you can see the door has no handle, but when Rocky draws a gun and goes to see Bugs, a handle appears from nowhere.
Continuity mistake: The view out the back of the barn door when it's first revealed does not match the same view, just minutes later, in the final shot of the film. (01:55:43 - 01:59:12)