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.
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.
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".
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.