Operation -- Annihilate! - S1-E30
Continuity mistake: After Kirk orders Uhura to reestablish contact with Aurelan's transmitter, when Uhura replies that they do not acknowledge her contact signal, Uhura's communications earpiece is not in her ear, but in the next shot it's suddenly back in her ear. (00:06:10)
Operation -- Annihilate! - S1-E30
Continuity mistake: When they put the satellites in orbit, Sulu announces they are in place. Then Kirk says "Energize" and the next shot shows the helmsman station and Sulu is absent - some guy in a red shirt is there instead. (00:45:30)
Operation -- Annihilate! - S1-E30
Continuity mistake: When Uhura tells Kirk that she's made contact with his private transmitter she's seated at the communications console, with the two overhead screens above her station, beside the turbo lift alcove. Yet after the contact's been broken, when she tells Kirk, "It's impossible at the moment because they stopped broadcasting," in this unusual shot facing Uhura the turbo lift alcove is not behind her - Uhura is actually seated much closer to Spock's station, note the upper section with overhead screens. Then she's properly seated at her station once again.
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.