Jim's white sweater is randomly clean, dirty, or very dirty as the movie progresses.
During the first scene at the school, how would tossing an explosive device down a toilet cause a surge of water out of a drinking fountain? Toilets should lead into the sewer. Are they drinking toilet water?
Pure sodium tossed into a toilet bowl would not result in a surge of water pressure around the building. It would most likely spark, smoke, and blow the bowl up almost instantly after contact.
Officer Marks is wearing a vintage style NY police badge on his hat, despite the fact that the story does not take place in NY.
Starting at 52:23 the wide angle shots of the chainsaw clearly show the chain is not moving.
After the alien brain eats the woman, dude's quote "That's food for thought" really doesn't make sense.
The dialogue implies that the story takes place in the US, but the road signs are obviously Canadian.
In Becky's room when she notices powder puffing out of its container the camera changes to the container and a hole is clearly observed where air is blowing the powder.
When The Brain informs Dr. Blakely via the video monitor that "Majelewski is here", the name is misspelled "Majeweleski".