The Corbomite Maneuver - S1-E11
Visible crew/equipment: After the Fesarius destroys the recorder marker, when Balok declares that Enterprise must also be destroyed, in the next wide shot there's a tape mark on the floor near Bailey, and another one in front of Kirk's feet. (00:21:50)
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.