Visible crew/equipment: When Kirk is agonizing over the sound of Surak's supposed cries for help, an equipment shadow, possibly from a boom mike, skates across the rocks behind his left shoulder. (00:40:00)
Visible crew/equipment: The shadow of a boom mic is seen against the rock walls of the cave follows Spock and McCoy when Spock pulls McCoy off Zarabeth.
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.