Plot hole: When Ripley goes to access the computer Mother, the entry door opens and closes with a hissing noise, a couple of minutes later you see Ash next to Ripley with a smile on his face. How did Ash manage to open the same door without it making the hissing sound? Ash could not have been in the room before Ripley came in - once Ripley has sat down at the console, it rotates on a 90 degree angle, this would have made it impossible for Ash to be hiding behind a desk or a computer console without being seen by Ripley. There are many doors on the ship that make the same hissing sound when the doors open, an obvious example is the infirmary door. And Ash couldn't have disabled the pneumatics of the door, because when Ripley exits the room, the hissing noise is heard again. (01:18:40 - 01:20:00)
Plot hole: When Jack The Ripper checks his watch before confronting H.G. Wells and demanding the key, the hands point to 8:50, the ensuing chase to the museum and demise of the Ripper may have used up a half hour or so, yet the time on the wall clock indicates that it is midnight.
Suggested correction: Movie time and real time don't match, so 3 hours has passed without all 3 hours being shown. The fact that the clock now shows midnight is meant to explain this fact without the need for subtitles to reveal the time.
Plot hole: In one scene saboteurs rig the Concorde's cargo door to automatically open suddenly in flight, on the principle that the rapid decompression will cripple the airplane & cause it to crash. At the critical time the door does start to open, but jams and only opens very slightly. Minutes go by, with the ajar hatch allowing air to freely pass through. Then, suddenly, the door unjams, and the compartment is shown losing air pressure dangerously fast. Problem is, that since the door had been cracked open for several minutes, the air pressure would surely have gotten to equilibrium by that time. (01:32:45 - 01:36:30)
Plot hole: When Ward's son hits the switch marked "Do Not Touch This Switch", every light in the amusement park comes on, music starts playing, and the rides all start moving. It's a funny gag, but it seems unlikely that one switch would power every single thing in the amusement park, and that everything in the park has been left on "full speed." If that's the case, when Angelo first sent the two lookouts to the top of the ferris wheel, everything else in the park should have come on then too.
Plot hole: Though there's supposed to be a championship football game taking place near the end of the movie, the stadium is strangely devoid of fans. A meager effort was made to fill some seats, but most of the shots show empty ones. It also looks as if the production crew tried to save money by using only half the stadium lights.
Plot hole: Mr. Elliott calls his office in Cleveland, Ohio from the secret pay phone in the lobby, but gets no answer. His wife explains it's 4 AM in Cleveland and that's why nobody answered. However, the island is somewhat close to Hawaii and the time difference is 6 hours during summer. The local time on the island would be around 10 PM. Outside however, the sun is shining. Not possible at 10 PM in that region.
Plot hole: When the Bigelows call Sackett out, Cap rises from his sickbed, takes a double-barrelled shotgun from over the door, breaks it open, and despite having used only a rifle and handgun up to this time, removes a couple of shotgun shells from his pocket and inserts them into the weapon.
Plot hole: Supposedly the plague broke out the moment the rats poured into the docks, as well as the plague breaking out when the rats got on the boat. However, these are domesticated rats. Only the fleas on black rats would carry the "Black Death," which is spread by fleas that aren't carried by other rats.
Plot hole: How did Professor Krassman get shocked into being a frog? The electronic device doesn't even touch his head.