Continuity mistake: When Chekov sits outside the general store chatting with Sylvia, his left arm and her right alternate from entwined to un-entwined and back again as the shots change. (00:27:40)
Continuity mistake: On the bridge, watch Uhura. She goes from both hands on her controls, to left hand on her earpiece in a split second.
Continuity mistake: At the end, on the Bridge, when the warning marker explodes, Kirk's arm shifts position between shots.
Continuity mistake: When Scotty inhales the gas, the amount of smoke changes between shots.
Audio problem: The bartender comes over and brings whiskey and five glasses, but we hear six glasses hit the table.
Factual error: Throughout the episode, there is a constant reference to 5 p.m. being the time Kirk and crew (a.k.a., the Clanton gang) were to die. However, the real 30-second shootout was at 3 p.m.
Answer: Kirk was getting his physical and Dr. McCoy probably turned off communications, because if he hadn't, Kirk would have left and headed straight for the bridge, leaving McCoy irritated.