Goofs

When asked for the town's population, the figure is stated as 10,001. The population on the sign shown at the beginning is 10,079.

The town sign writer is not doing his job.

When the last alien gets killed by tail rotor of the chopper near the end of the film, it's clearly visible all of the blood and guts of the alien splattered over the tail of the chopper. After the chopper's landing, it's all gone.

After Jarvis is captured and searched, an agent hold up a 3.5" floppy disc which he says contains their plans to handle scenarios like this. He's holding the floppy up with one side facing him and the other facing the Old Man. When we see the agent from the front, we see the bottom of the floppy. When we see over his shoulder, we still see the bottom of the floppy. He'd have had to turn it over in his hand repeatedly for it to look like this.

At the end of the film, the large blood spot near Sam Nivens' right eye tends to appear and disappear on different shots.

When Sam is being interviewed in the hospital by his father, one shot shows another patient in the bed behind his father, but at the end of the scene a wide shot from above shows the bed is empty.

In the scene where the monkey gets infected by the alien and starts typing, the keys he presses do not match what he is writing.

It is hard to tell because after the first few test keystrokes, the camera wasn't looking at the keyboard when the monkey typed the actual text.

After the president is saved by the OSI agents, just after Donald Sutherland enters the room a crew member's hand can be seen catching the door.

Near the end of the movie, as a helicopter lands at the "Des Moines" City Hall, tall palm trees are visible in the background.

Graves compares how the aliens raise their hosts body temperature to injecting nitro (nitrous oxide) into a car's fuel line to make it run faster. NOS isn't injected into a fuel line. It is added to the air or the air/fuel mixture that goes in the engine. There it decomposes due to heat, thereby adding oxygen. Extra fuel can thus be used for a more powerful combustion.

At about 27 mins, when Sam unbuttons his shirt, he unbuttons only the top one; the others are already unbuttoned.