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.
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)
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.
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.