Visible crew/equipment: As Kirk gives orders to Nomad to lower screens for Spock to examine it, the shadow of the boom mic is toward the top of the screen behind Nomad. Also, the wire holding Nomad up is visible.
Continuity mistake: When Nomad initially attacks the Enterprise, Uhura appears/disappears in subsequent shots of the bridge.
Revealing mistake: When the Enterprise is attacked in the prologue, some of the crew grab onto the central console (that Sulu and Chekov usually sit at). The console noticeably lifts up from the stage surface, almost falling over. Twice.
Continuity mistake: After Spock mind melds with Nomad, Kirk hustles him out into the corridor. In the shots taken from behind Kirk, the Captain's left hand is high on Spock's shoulder. In the reverse angles, his hand is several inches lower on Spock's arm. (00:35:00)
Continuity mistake: When Nomad first appears on the bridge, the indicator light on Scott's communicator panel is on. A second later, it's off, and he turns it on to say his line.
Revealing mistake: A number of times through the episode, the wire holding Nomad up and moving it around is visible. Example: When Nomad first moves off the transporter pad, look directly above it; the black wire can be seen in front on the light over the pad.
Visible crew/equipment: When Kirk walks into the brig Spock tells him that Nomad has almost human stubbornness, and that its screens are still up, then just as Kirk moves closer to Nomad the shadow of the moving boom mic is visible at the top, left side of the screen. (00:28:15)
Continuity mistake: As Nomad first hears Uhura's singing, it extends antennae and leaves the room. After a quick cut scene, as it turns in the corridor the antennae is retracted, then out again on the bridge.
Visible crew/equipment: When the camera looks at Spock after Scott's body is removed from the bridge, the shadows of lighting equipment is visible behind him.
Continuity mistake: When Kirk and Spock get to Sick Bay, the doors open to reveal Nomad coming out. But the shot of Nomad coming out is a re-used shot of it coming out of the Turbo Lift, not the Sick Bay, as the nameplate said. (00:42:10)
Continuity mistake: When Scotty awakens in the sick room after being attacked by Nomad, Nurse Chapel has her hands placed on him. In the next shot, when McCoy tells Scotty to take it easy, Nurse Chapel's hands are no longer on Scotty, and in the next shot, her hands are back on him.
Revealing mistake: When Kirk, Spock and McCoy study a diagram that shows various parts of the Nomad probe, the lower right of the diagram reads "Computer Data Banks Recall & Transmition". It should read "Transmission".
Continuity mistake: When the security team is escorting Nomad back to the holding area, he goes his own way. One of the team then says, "Hey Nomad!" and begins to reach for his phaser. But in the next shot, he has already got his phaser out and trained on Nomad.
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.