The Return of the Archons - S1-E22
Continuity mistake: After Kirk and the landing party beam down, they are met by a man who tells them where they can stay for the night but they will have to hurry because it's almost the "red hour." At that time the camera shows a clock that reads 5:58. After being introduced to the daughter of the man who can give them shelter, a gong rings and magically it is 6:00, 2 minutes later, although only 32 seconds of real time has passed. (00:05:18 - 00:05:50)
The Return of the Archons - S1-E22
Continuity mistake: In the exterior shot, the double front doors of Reger's house have large curtained windows in them. After the Enterprise landing party rushes inside and closes the doors, however, they're suddenly solid wood with no windows. (00:06:35)
The Return of the Archons - S1-E22
Continuity mistake: After the Law Giver kills Tamar, he starts to raise his staff. When the camera is in a close up on the Law Giver a second later, it's straight out again. (00:13:15)
The Return of the Archons - S1-E22
Continuity mistake: As Captain Kirk talks to Dr. McCoy, the background changes from stone to a red background in a closeup of Kirk's face. (00:27:05)
The Return of the Archons - S1-E22
Continuity mistake: The lawgivers' robes that Kirk and Spock take off and drop on the floor just inside the doorway disappear after they phaser the wall to reveal Landru. The robes reappear a few minutes later, but have now migrated several feet to one side, bunched up against the wall where they are no longer in tripping range of the actors about to enter the scene. (00:42:25 - 00:45:00)
The Return of the Archons - S1-E22
Continuity mistake: The U.S.S. Archon wasn't violating the prime directive, the prime directive was formed in 2253.
The Return of the Archons - S1-E22
Continuity mistake: As Marpon talks to Spock, his right hand goes from being palm forward toward Spock, to being vertical, palm open, thumb upwards, and back.
The Return of the Archons - S1-E22
Continuity mistake: As Kirk talks to an "absorbed" McCoy, in the back-and-forth cuts between them, the part in Kirk's hair jumps from left to right and back.
The Return of the Archons - S1-E22
Continuity mistake: While Kirk is attempting to convince Marplon and Reger to take them to Landru, a distant shot shows Marplon's right hand descend from his chest to his side. Immediately thereafter, a close-up shows Marplon's hand again suddenly at his chest.
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.