Captain Spock: If I were human I believe my response would be "go to hell." If I were human.
Commander Pavel Andreievich Chekov: Course heading, Captain?
Captain James T. Kirk: Second star to the right and straight on till morning.
When Captain Kirk and the shape shifter are fighting on the planet (the shape shifter looks exactly like Kirk). They are rolling through the snow about to roll over Bones. In one shot, it looks like they will roll over his feet first, and then the rest of his body. In the next shot, it is a little closer and they roll over Bones' right arm first and not his feet first.
Both the opening explosion of the Klingon moon Praxis and much of the footage from the U.S.S. Excelsior was later used in an episode of "Star Trek: Voyager", ("Flashback") with special guest star George Takei.