The Ultimate Computer - S2-E24
Visible crew/equipment: After M-5 fires on the other starships Daystrom speaks to M-5 about the murders, then when Kirk walks over to Daystrom and tells him the M-5 must be destroyed, the shadow of the moving boom mic is visible over Daystrom. The white tape mark is also visible on the floor near Uhura's chair, where McCoy had been standing earlier. (00:42:15)
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.