Continuity mistake: The Bird of Prey is the one captured by Kirk's crew in ST III. That ship's bridge showed Klingon Cmdr Kruge in his elevated command chair with his helmsmen arrayed circularly below him, and nothing else. ST IV has this same ship; however, the bridge now resembles The Enterprise layout with Kirk's command chair behind Sulu and Chekov at their rectangular helm, with Spock, Scotty, and Uhura at their usual positions.
Suggested correction: According to the captain's log at the beginning, they have been on Vulcan for 3 months. As they prepare to depart, we see several Vulcan technicians moving equipment in and around the ship. It's quite conceivable that the bridge was reconfigured according to the crew's specifications to facilitate their use of the ship. This may seem a bit excessive, as the remodel includes the door onto the bridge, and the frame of the door, and possibly most of the rest of the ship. But it's not outside the realm of possibility. The real mistake, though, is why they would go to the effort of installing new workstations on the Klingon bridge and marking them with Klingon labels, instead of standard Federation text. Interestingly, though, the "Starfleet" style bridge layout of the Klingon ship is being used by the Klingons on the Bird of Prey in Star Trek V.
Continuity mistake: When the old man is talking to Chandler on the porch in Tibet, he picks his nose with his pinky finger. When it cuts back to him, he's picking with his index finger instead. (01:04:30)
Continuity mistake: In the scene where Dr. Dawson and Olivia are seeking Basil's help at his house, Basil sits down and starts playing the violin, holding it in his right hand and having the bow in his left. When Basil the stands up in another shot, he is holding the violin in his left hand (like it's supposed to be) and the bow in his left.
Continuity mistake: At Ben's place, Frank enjoys a cold glass of Pabst Blue Ribbon - its colour, the level in the glass, and the amount of head change repeatedly within a few seconds.
Continuity mistake: When Jim and Brandon are knocked into the water, Brandon dies, but somehow manages to grab hold of Jim and pull himself up.
Continuity mistake: When Harry Mitchell is at Leo's club with Doreen, he takes a Polaroid of her. When she asks him how it came out and he tells her it's a little dark, he's actually looking at the picture upside down. We then cut back to Doreen then back to Harry, only this time he's holding the same picture the right way up. Also, during the same scene, Doreen's suspender belt starts off attached to her stockings, then it's unattached, then attached, before we see her unattaching it.
Continuity mistake: In the scene where Remy finally figures out that Ann has some serious questions about his dept., he pushes her against a tree. When the camera is on him, her necklace has swung around to the back of her dress. When the camera is on her, the necklace is 1/2 inside and 1/2 outside the front of her dress. This switches back and forth several times.
Continuity mistake: After Eugene takes the stage to face Jack Butler, everyone (including Eugene) turns when Scratch walks into the room. When Scratch sits down and Eugene turns back to face Jack Butler, Eugene's hat is gone.
Continuity mistake: To reach Poirot, Hastings walks through the Acapulco airport with two ladies (one with a white jacket, light blue skirt, updo, carries a large brown suitcase, and another one with short hair, glasses, white trousers) that are both in front of him AND behind him, depending on the camera angle. (00:01:30)
Continuity mistake: Jane Fonda gets out of Jeff Bridge's car in broad daylight, but when she enters the dead man's house, it's night-time.
Continuity mistake: Poirot met Ariadne Oliver who invites him to the "murder hunt." Poirot and Hastings then get on a boat to head there. As they sit on the boat, there are a few extras, led by an easily identifiable lady in a yellow sweater, that move up the stairs of the pier and reach the top. The boat slowly takes off, and about 10 seconds later we see the pier again, with again those same people from before just reaching the top of the stairs. (00:02:25)