Continuity mistake: While avoiding the glowing meteoroid, they decide to fire their jets to push them into a higher orbit. In a couple of scenes they go up but a third one has them going back down.
Continuity mistake: Mantee finds a pool of water after falling through a hole. He gets in nude, but you can see him wearing tan-colored trunks during the close-ups. However, the far away shots do show him naked.
Revealing mistake: The ground beneath Mantee's feet gives way with him falling through the hole. Boy, that hole sure looked rectangular.
Visible crew/equipment: Paul Mantee's helmet reflects two stage lights often when he is supposedly outside.
Factual error: Draper consults a recorded video-lecture on survival tips while on Mars. Behind the lecturer is a chalkboard with two force laws from physics written. One is Newton's law of gravity, the other is Coulomb's law for electric charges. The constant of proportionality for Coulomb's law is given as e0, whereas this is really only one component in the whole expression for the constant, 1/e04pi.
Revealing mistake: Early in the film, when Commander Chris Draper is still wearing his space gear on the Martian surface, multiple helmet reflections reveal that at least two and as many as four powerful artificial light sources (in addition to the Sun) were used to illuminate the exterior scenes.
Revealing mistake: Several scenes used a fake monkey to protect the live one from injury. The "stunt monkey" is most obvious in the scenes where Draper is climbing the steep cliff walls with the mannequin attached to his rucksack.
Other mistake: The abandoned orbiter requires fuel to decelerate and drop out of its stable orbit. Mantee knew the orbiting spacecraft was out of fuel before leaving it, but he was still trying to give the craft voice commands to land some forty minutes into the film.
Answer: In the movie before he discovers his water supply and watches the survival video, he is shown grooming himself and shaving.