Continuity mistake: The hilt of the blade Kirk holds against Tracy's throat is close to Tracy's jawbone in the close ups and further away in the long shots.
And the Children Shall Lead - S3-E4
Continuity mistake: When Gorgon the Angel is on the bridge with the children, the positions of the children are different depending if the shot is from the rear of the children or the front.
Revealing mistake: As the camera is close to Dr. Sevrin, the line of the bald skin wig is easily seen.
Revealing mistake: Kirk uses a sword to cleave a Roman guard during his escape from the TV studio, but there is no blood on it. Later, though, when Claudius stabs Merrick in the back, there is blood on the knife blade.
Revealing mistake: Kirk uses a submachine-gun to shoot the lock of the cell holding Spock and McCoy, but no bullet holes appear, nor is the lock damaged.
Revealing mistake: A Roman guard empties half a magazine of bullets from his submachine-gun into Flavius, but there are no bullet holes in his body, nor blood on the floor from the wounds inflicted by the bullets.
Visible crew/equipment: Set lights are reflected in Spock's tricorder screen before he closes the cover.
Let That Be Your Last Battlefield - S3-E15
Revealing mistake: As Kirk turns all the way around to look at the newly arrived Bele, the shadows of the stage wiring is easily spotted at the top of the screen.
The Enterprise Incident - S3-E2
Continuity mistake: When the guard opens the cell barrier, the light bars turn off, then slide back. As they come back out, they're already on, rather than the reverse of the opening procedure.
Continuity mistake: To open the secret doors, Seven tilts one of the pen holders down to the top of the desk. After he's gone, Ms. Lincoln comes in looking for him, and the pen is upright without it having been pulled back up, unless it was supposed to reset itself.
The Enterprise Incident - S3-E2
Other mistake: As the Romulan commander goes to answer the intercom, the switch she touches to open the link is already on, probably left that way from a previous take.
Other mistake: In the cells, the particular strip of metal Kirk pulls loose has rivets that are noticeably different than the rest, making it easier to pull loose.
A Piece of the Action - S2-E17
Continuity mistake: The pistol Kirk is pointing at the gangster changes elevation and angle as the scene cuts between the front of Kirk and over his shoulder.
A Piece of the Action - S2-E17
Continuity mistake: The scene outside shows a guard standing close to a sign on the wall that says, "Jo Jo Krako", but the next overhead shot shows the guard further away, and a railing between the sign and the guard that would have prevented anyone from getting close to it.
A Piece of the Action - S2-E17
Continuity mistake: When Krako's men are in the gun battle with Bela's men, the Enterprise stuns them with its phasers. The number of bodies and their positions change after the men are stunned.
Continuity mistake: In the reception room, Amanda's glass goes from 1/4 filled after McCoy poured more, to over 3/4 full without his adding more.
Continuity mistake: After landing on the planet, the interior walls of the shuttle craft or well-lit, and light green in color. As Kirk and party exit, the interior is seen to be dark and gray.
Continuity mistake: In Norman's chamber, the medallions on Alice 3 and 11 go from blinking to steady, to totally off and back to blinking through the scene.
The Return of the Archons - S1-E22
Other mistake: On the bridge, as the camera looks at the view screen, there is a flashing blue light reflecting on the console in front of Sulu, but there is no light other than scanner under the viewer flashing and it's too far away to project light that far, and it's amber colored.
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.