Just under an hour into the movie, at the conclusion of the scene where Drew (Kurt Russel) pours the contents of a can of beer over his head before leaving the house, watch carefully as he then walks out of the house and out onto the porch. He can be seen striking his head with considerable force on the porch, hard enough to produce an audible noise and would surely have caused a considerable amount of pain. In the next immediate scene and thereafter, no physical sign of injury can been seen on the actor.
Kerr McGee's Cimmeron plant is on the east side of Hwy 74, between Crescent to the north and Oklahoma City to the south. Opening scenes show a mileage sign for Crescent, which is really the opposite direction. This also causes incorrect footage for placement and direction of travel in later scenes (ex. placement of car in accident, tow truck pulling wrecked car past Crescent Cafe, etc.)
After Karen's first contamination, she and Drew are at home and Drew is laid out on the bed playing his banjo and black (X) marks can clearly be seen on the quilt. These are not actor position marks, but (repeating) parts of the quilt pattern. Drew's body lining up on the marks is just chance.