Revealing mistake: At the end, a special effects matte flaw causes the rear tip of the starboard side nacelle to vanish briefly as the Enterprise orbits Scallos. (00:45:50)
Revealing mistake: In the Enterprise lab, as a sped up Spock goes to move away from McCoy and Chapel, McCoy's eyes follow his movements rather than looking at where Spock was supposed to be after he "disappeared."
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.