Tomorrow is Yesterday - S1-E20
Character mistake: When first considering the impact of Captain Christopher's removal from this time, Spock makes a mistake in his dialogue. He says "They show no record of any irrelevent contribution..." when it should be "relevent..." (00:13:50)
Tomorrow is Yesterday - S1-E20
Character mistake: Kirk introduces Spock as "Lieutenant Commander Spock," but Spock is obviously wearing full commander's stripes on his uniform.
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.