Visible crew/equipment: After McCoy examines Charlie and they talk about how Charlie learned to talk by just listening to the ship's tapes, when Charlie stands up the two actors' marks can be seen on the floor - the short one for Charlie and the longer one for McCoy, where they both will stand momentarily. (00:04:56)
Continuity mistake: When the Thasians restore Yeoman Rand on the bridge she's barefoot, but when Charlie begs Kirk not to let the Thasians take him because he can't live with them anymore, we see Rand wearing a white fluffy slipper (which she wasn't holding when she reappeared), then she's back to being barefoot again. (00:44:42)
Visible crew/equipment: When Charlie catches up with Rand and gives her the present, the microphone can be seen moving around at the bottom of the screen in the shots with both of them. (00:06:48)
Continuity mistake: When Capt. Kirk and Charlie enter the turbolift heading for the bridge, Kirk is wearing one style of tunic and when the turbolift arrives on the bridge, Kirk is wearing a completely different tunic. (00:15:14)
Visible crew/equipment: After Uhura tells Kirk that "Captain Ramart of the Antares is on D channel," Kirk and Charlie head to the bridge, and when it cuts to Uhura the actor's tape mark can be seen on the floor behind her, where Charlie will stand when he steps out of the turbolift.
Continuity mistake: In Janice Rand's quarters, Charlie mentally throws Kirk and Spock against the wall. After they collide with it and slide down the face of the wall, there is a huge indention and crack where Spock hit. After a camera cut to Charlie, when the camera looks at Kirk and Spock again, there is no damage to the wall. (00:36:52)
Continuity mistake: After Sam tosses Kirk, he goes to a bench in the corner, picks up the towel that was there, and sits down. After Kirk tosses Charlie, Sam is laughing, and Charlie makes Sam "go away." After Sam fades out, the towel that he had around his neck is lying there, when it disappeared with Sam. (00:27:36)
Continuity mistake: Uhura starts to sing and walk around Spock as he plays. In Spock's close ups, the wall behind him is pink and green, but in the further shots the walls are a blue color with nothing behind him that could have been making the green and pink colors in the close ups. (00:10:50)
Continuity mistake: After Spock and Kirk attempt to trap Charlie into a room with a force field, Charlie makes the wall disappear and then freezes Kirk and Spock in place. Spock has his right hand against the wall at about chest level with himself. The camera cuts to a closer angle and suddenly his hand is higher up, about face level. (00:39:47)
Continuity mistake: When Kirk begins to question Charlie about the melted chess pieces, there is a close up of Kirk showing light cast down him him with his chest void of any shadows. When cut to a wide angle, he suddenly has shadows on his chest from lighting changes. (00:22:36)
Continuity mistake: Just before Uhura begins to hum with Spock's playing of his instrument, she is leaning over a table where they are playing cards. She has one hand on her cheek and then brings the other up to her face as well. When it cuts to a side angle, she's suddenly bringing her hand up to her face again in a repeated action. (00:09:47)
Revealing mistake: As Charlie watches the pole lowering into a square hole in the deck, the wood grain of the set piece is visible. The wood has been painted gray/silver to look like metal. (00:06:06)
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.