Continuity mistake: The sign on the door that was blocked by the fork lift truck gets half knocked off by a spider; then you see it intact. (01:20:55)
Factual error: In the mine, David Arquette and the others start to smell the methane gas and one of the people even quips "It wasn't me." However, methane is an odorless gas and therefore they probably wouldn't have had any way to tell if it was there. (01:21:55)
Continuity mistake: Towards the end when Chris and Gladys escape the giant spider in the mine on a motorbike, Gladys picks up a helmet and says to Chris, "I need this more than you". The helmet she is holding has a cobweb on the cage at the front. But once she gets on the bike with Chris, the cobweb has disappeared.
Visible crew/equipment: In the beginning of the movie, when the kid goes for the first time to the spider farm, you can see the camera and crew reflected on the glass of the spider tanks. This is seen when the kid is looking for the owner of the spider farm among the tanks.
Factual error: Due to the way in which a spiders respiratory system works it would actually be impossible for the spiders to breath as their box lungs would collapse and their primitive circulatory system wouldn't get enough oxygen around the body.
Answer: Both! The owner of the spider farm was feeding the spiders bugs from the water that had the chemical spill in it. The bugs were contaminated with the chemical, thus contaminating the spiders. Note: The man who owned the spider farm had no idea about the contaminated water.
SAZOO1975