The Man Trap - S1-E2
Revealing mistake: In the corridor, as Sulu touches the face of the dead crewman, the man's eyelids flutter. (00:30:15)
The Man Trap - S1-E2
Revealing mistake: On the planet, as Kirk and Spock try to get to Professor Crater, Crater fires at and destroys the center support of the arch. As it settles, the parts are clearly hollow. (00:34:21)
The Man Trap - S1-E2
Revealing mistake: Just after Kirk stuns Crater with his phaser, he gets up to get to Crater, when he does he bumps into a heavy stone monument,a prop that shakes visibly on contact. (00:36:58)
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.