Gaffes

Quaid touches walls, switches on lights, and grabs Lori's arms to explain that he is being hunted by spies, then shows his blood-covered hands to her, yet there is no blood on her arms or the walls.

During Quaid's fight with Lori in the apartment, Lori slashes Quaid in the chest with a knife. After the fight, the cut marks on his shirt are mysteriously gone.

During the escalator shootout, Quaid uses a bystander's body as a bullet shield and the body is shot to pieces; Quaid then throws the very bloody body onto Richter and his henchmen to slow them down. Moments later, as Richter and his henchmen chase Quaid into the train station, it is obvious that they don't have a drop of blood on them despite the fact that the bloody corpse landed right on top of them.

At Rekall, when Dr. Lull is questioning him about his dream girl, Quaid's request of "sleazy" and "demure" are highlighted on the monitor before he says them.

When Richter and Helm are waiting by the hotel's service elevator for Lori to bring down Quaid and realize something is wrong, they run over to a normal elevator and go up, yet they end up coming out of the service elevator on the sixth floor.

in the construction scene, many construction workers operating jackhammers are shown to be wearing hard hats and ear protection for obvious safety reasons. Doug and Harry are wearing neither.

The exterior shots of Mars depicts the Martian sky as having either a dark orange or deep crimson color to it. In reality, the Martian sky is not as deeply colored and is actually a light pink or light orange color at times. Furthermore, the night sky on Mars is shown to be just a slightly darker red/orange than the day sky, when in reality the Martian night sky is just as black and starry as it appears on Earth.

The two moons of Mars appear in several background shots, but they are incorrectly depicted. They are both shown as being much larger than they would appear in real life. Phobos would appear to be about a third of the size of the Earth's moon, and Deimos would be a little larger than a "star". In addition, Phobos orbits Mars faster than Mars rotates, so it would appear to rise in the west and set in the east, and should have moved visibly with respect to Deimos even from one shot to the next.

Towards the end, Quaid and Melina are flung out into the raw atmosphere of Mars, and their eyes and tongues start to swell from the pressure. When the newly breathable atmosphere envelops them, their faces return to normal even though they should be showing signs of injury from the broken blood vessels, etc.

The first name of the author of the original story (Philip K. Dick) is misspelled as "Phillip" in the credits.

The soldiers are all wearing what appears to be bulletproof vests, but they don't seem to stop anything.

Even in real life, "bulletproof" vests do not stop all forms of ammunition.

At several points in the film, characters either shoot at the glass in the Martian domes and crack it, or are advised against doing so. It seems odd that this futuristic, space-faring culture would not install bulletproof glass in these domes, given the dire results of the windows being destroyed.

Throughout the movie, several references are made to Cohaagen constructing Mars Colony by cutting corners, building cheap domes, and pocketing the cash for himself. Also the cheaply-built domes not adequately filtering out the solar radiation explains the mutant population on the planet.

Dissolving ice either by evaporation or hydrolysis would not provide a breathable atmosphere. Evaporation only gives you steam, which is not useful oxygen. Hydrolysis would give you an atmosphere of hydrogen and oxygen which is highly explosive! Any spark or flame would pretty much turn the gases into water (back to ice), killing anything in the area with the highly exothermic reaction.

We do not know what other technology the ancient, and obviously far advanced, aliens have constructed to compensate for these discrepancies.

Richter and Cohaagen have a videophone conversation in a car. Unless they have some future technology which can overcome physical laws, one cannot have a conversation with someone on Mars from Earth without a delay of about 12 minutes between transmission and reception of signals. The speed of light and distance to Mars prohibits a real-time conversation.

Clearly then, they have some future technology which can overcome physical laws.

Due to the small size of Mars, there isn't enough gravity to retain an atmosphere. So even if an atmosphere were artificially created, it would float off into space and all those people would still suffocate.

Clearly the ancient and advanced alien species who constructed the device designed some way for Mars to retain its new atmosphere.

When Quaid is removing his woman mask, a part from the ear extends that goes in way too deep for his actual head to not be in the way.

The security guards wear some kind of portable computer (display and keyboard) on their wrist. During the fight at customs, a close-up reveals that it's just a Sharp pocket calculator taped to a glove.

When Richter is shooting at Quaid from the top of the escalator, Quaid uses a human shield then turns and throws the body at the goons on the escalator below him; you can see the stuntman's eyes open and face cringe as he flies through the air.

When Quaid and Richter are fighting on the elevator, Quaid throws Richter into the back of the elevator and it wobbles, revealing it's made of soft material.

When Richter shoots the glass dome, Quaid grabs hold of the handrail. In the close-up of Quaid, visible wires are attached to Quaid's body.

Publicity is misspelled as "Publicty" in the end credits.

When Benny gives the other taxi driver the finger and says "Eat this!", the audio is not in sync and he is saying something else.

While Doug writes Melina's name on a piece of paper, the sound of the writing isn't in sync with the hand movement.

When Dr. Edgemar and Lori are with Quaid in his room at the Mars Hilton, lighting equipment for the scene is visible as a reflection on the double sliding glass door mirrors.

As Lori exits her bedroom, just after her image is visible in the mirror, a crewman wearing a white t-shirt is briefly visible in the same mirror.

Person's head visible behind bed during first sex scene.

Richter and his henchmen pump nearly a hundred bullets into the Johnny Cab, breaking the windows at the same level as Quaid is sitting, yet he doesn't suffer even a scratch.