When the nurse enters the room of the melting man, she drops the blood containers and it splatters her shoes; then, as she runs away down the hallway, her shoes are completely clean.
Two different Saturn rockets with two entirely different payload configurations are used for the launch sequence at the end of the movie.
While the Melting Man is creeping around, the sunlight changes between shots from late sundown to mid-afternoon, and then immediately to the middle of the night.
Sheriff Blake only has a revolver when he talks to the bums along the railroad and then, minutes later, he also has a shotgun.
When the nurse enters the room with the blood and sees Steve West, she drops the blood and runs screaming through the hospital. Later, she is running in slow motion, and she has 4 scratch marks on her right cheek, as if Steve reached out and scratched her face, and there's correlating blood on her uniform. But Steve never got close enough to even touch her before she got outside.
Saturn is a gas giant and has no surface to speak of, just millions of square miles of clouds. This means it is literally impossible for a spacecraft to land there.
At the beginning of the movie, the astronauts at Saturn are seen communicating with Mission Control at Houston instantaneously. In fact, the communication time lag between Earth and Saturn is roughly two and a half hours.
Saturn's rings are composed of icy debris. A spacecraft flying through them would more than likely be smashed apart long before a mysterious phenomenon could cause its crew to melt.
It is implied that Judy is pregnant, yet she uses sedatives & drinks wine, though the two can cause birth defects. Her mother's boyfriend informs that she shouldn't eat candy during pregnancy: but indulging in your cravings is okay in moderation, as long as you are not omitting more nutritious foods.
When the nurse (frightened by the sight of the Melting Man) smashes out a glass door of the hospital, there is no stock smashing noise.
During the hillside photo shoot, the actor's finger is nowhere near the shutter release, but the sound effect of an auto advance continues throughout the scene.