Continuity mistake: After Spock's Brain is taken McCoy says he has no idea how long the body can last on life support without the brain. Somehow in the following few moments McCoy has established that Mr Spock's Body will die in exactly 24 earth hours. No explanation is given as to how he came up with this figure.
Continuity mistake: When Kara renders the landing party unconscious, Kirk falls with his arms splayed out to each side. But in close-ups, he has one hand folded over his chest. (00:23:30)
Continuity mistake: In the beginning Chekov disappears off the bridge for a moment and is replaced by a blond haired crew member, then he returns.
Continuity mistake: When Scotty, Kirk, and the others follow Spock's signal to the chamber with the Controller, they encounter Kara and she activates their pain bands. Spock's body has a pain band around his waist as the other men drop to the ground, but after McCoy tells Kirk, "Spock, no pain," the pain band is missing from Spock's body, then in the next shot it reappears when he goes after Kara's bracelet. (00:35:05)
Continuity mistake: When Kirk and his landing party beam down to the planet there are six shots of Morg, who have their right arms covered in fur in all those flipped shots, but when Morg attack the landing party it's their left arms covered in fur. Presumably, the first six shots were flipped for direction continuity. (00:13:15)
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.