Mira is supposedly weightless in the pressure chamber, but her tunic skirt remains perfectly flat and her long hair doesn't even float - it's hanging straight down below her head.
When the landing party beamed down to the library planet after the "storm" hit, Kirk's voiceover said it was an "onimous" sign, instead of "ominous". "Onimous" isn't even a real word.
Kirk has Romaine put into the pressure chamber and increases the pressure one atmosphere per second. At that rate, she'd have been flattened more than a pancake in under a minute.
Scotty had a science patch on instead of the engineering patch in the episode.
Watch after one of the briefings when Kirk heads for the bridge. The briefing room door opens and an extra is standing outside, stock still, then immediately "unfreezes" and starts walking - apparently the extra missed his cue.
Kirk orders Sulu to evade the Zetars by turning to starboard and the creatures drift off the screen to the left. But then they come back on to the screen from the left, which doesn't make sense unless they circled all the way around the ship. Then Sulu turns the ship to port and the same thing happens, screwed up in reverse.
When Kirk goes to Memory Alpha there's a dead man with a viewscreen near his right shoulder - the shot changes and now it's near his left shoulder.
What's the point of making Romaine weightless in the pressure chamber? They exist in a vaccuum and McCoy and Spock both say they're getting stronger now that Romaine is weightless - so why do they just leave her floating there?
Scotty discusses Romaine's visions with the crew and says she foresaw the first attack on the ship - she never said anything about the first attack to him previously (a cut scene, perhaps?).
Kirk: Scotty, where've you been? Where are you?
Scotty: In the sickbay.
Kirk: Are you sick?
Scotty: Oh, no. I was just checkin' on the lass. She's going to be fine. There's nothing wrong.
Kirk: Well, I'm relieved to hear your prognosis, Mr. Scott. Is the doctor there, or will I find him in Engineering?
McCoy: Somehow I find transporting into the darkness unnerving.
Kirk: (speaking into his Captain's log) When a man of Scotty's years falls in love, the loneliness of his life is suddenly revealed. His heart once throbbed to the sound of the ship's engines; now all he can see is the woman.
Chekov: I didn't think Mr. Scott would go for the brainy type.
Sulu: I don't think he's even noticed she has a brain.
Sulu: Captain! The storm is approaching us at Warp 2.6 and accelerating.
Kirk: Check that! No natural phenomenon can travel faster than the speed of light.
Spock: It is definitely doing so, Captain. Therefore it cannot be a phenomenon of nature.
Kirk: Well this is an Enterprise first. Dr. McCoy, Mr. Spock, and Engineer Scott find themselves in complete agreement. Can I stand the strain?
Kirk: Bones, are you able to judge the long-range effects on Lt. Romaine?
McCoy: When the personality of a human is involved, exact predictions are hazardous.
Spock: Particularly where humans are involved.
Spock: (talking about love) Humans do claim a great deal for that particular emotion
The second-season end-title theme music returns for use in the last 7 episodes of the third season.