Continuity mistake: When Elaan visits engineering, the close-up shots of Scotty show a security guard wearing a black utility belt standing in the background. But the man is missing in all the full shots. (00:13:15)
Character mistake: Elaan says "If I have to stay here for ten light-years..." A light year is a measure of distance. (00:24:03)
Revealing mistake: During the battle scene, the use of special effects stock footage of the view screen, as seen over the helm from the opposite side of the bridge, briefly turns the short, brunette Ensign Chekov into a tall, thin blond guy. (00:44:20)
Factual error: Spock says the Klingon ship is approaching at Warp Six, but Sulu counts off the distance at about 50,000 kilometers per second - that isn't even the speed of light.
Continuity mistake: As Kirk wipes a tear from Elaan's face, both cheeks are wet. A second later, both cheeks are dry.
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.