Visible crew/equipment: When Scotty joins Thalassa while she's working, she asks if he has "prepared the megaton hydrocoils," and the shadow of the boom mic can be seen moving at the top of the screen. (00:33:20)
Continuity mistake: Why does Kirk think a being of pure energy is "impossible?" They've encountered several such creatures in the past in "Metamorphosis," "Obsession," and "Wolf in The Fold."
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.