Visible crew/equipment: After Amanda tells McCoy about Spock's pet sehlat, when Sarek and Amanda walk away, the actors' multiple white tape marks are visible on the floor, under the table. (00:10:50)
Visible crew/equipment: At the hangar deck, after Kirk introduces Sarek to Spock and McCoy they all step forward, then as Sarek introduces his aides and his wife, the three white tape marks are visible on the floor behind them, where they had been standing. (00:02:15)
Character mistake: William Shatner mentions the sound enhancer is multiplied by 1 to the 4th. I think he meant 10 to the 4th.
Continuity mistake: After McCoy checks the Horta, he approaches Kirk with his tricorder in his left hand. The scene cuts to McCoy and Kirk and now McCoy's tricorder is in his right hand.
Continuity mistake: Spock and Kirk both arrive at the sizzling remains of a red shirt crewman, standing close together, but the next shot of the crewman's remains shows only one set of legs at the site (presumably Spock's), not two.
Revealing mistake: As Spock carries the crewman, the second spear hits a rock. As it does, you can see the Styrofoam chips fly up.
Factual error: The harpsichord Trelane plays is far too short and has pedals like a piano.
Revealing mistake: After being put in the cell, when the camera is in a closeup of Spock, you can see the lines in the prosthetic ears, and can easily tell where the makeup is blended into his real ear.
Continuity mistake: As Gary Seven beams in, Scotty's hair changes between shots.
Other mistake: Ben Finney's rank is stated as Lt. Commander. His rank insignia on his uniform shirt is that of Commander (The same as Mr. Spock whose rank is Commander).
Continuity mistake: As Mira is speaking with the alien's voice, Spock is behind a console that has a piece of equipment attached to it. From behind Spock, the piece is to his left, but the close ups of Spock show him close to and directly in front of it.
The Gamesters of Triskelion - S2-E16
Revealing mistake: As the camera does a close up of the Master Thrall, the line of the bald skin cap is visible. (00:05:10)
Visible crew/equipment: As Spock swings the scanner around, as it points toward the camera position, the camera equipment is reflected on the chrome plate on the front.
Continuity mistake: When Mr Hengist goes on the rampage in the hearing room, Kirk pushes Yeoman Tankris behind him. However, when we see Kirk punching Mr Hengist in the jaw in the next shot, Tankris is missing, and in the shot after that, she is back again.
Requiem for Methuselah - S3-E19
Other mistake: As the miniaturized Enterprise appears on the table, the support for the model appears as well.
Continuity mistake: When Nomad first appears on the bridge, the indicator light on Scott's communicator panel is on. A second later, it's off, and he turns it on to say his line.
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.
The Gamesters of Triskelion - S2-E16
Other mistake: Kirk tosses the Andorian, and as he hits the ground, his shirt comes up and the man's real skin tone is visible.
Other mistake: When the nuclear bomb explodes, the ship is tilted 40° to 45° to starboard (right), but Uhura goes over to the port (left) side of the lift.
Revealing mistake: As the Romulan ship is tilted, the dust and debris fall straight down, rather than diagonally toward the wall and floor joint.
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.