Factual error: With Irv and Blaire, one of them picks up the handful of popcorn and presumably eats the spider. While inside the eater, the spider would bite and poison whoever it was inside. When they find both of them dead, the spider crawls out of one person. Why would it leave one body and actually take the trouble to go inside the other rather than just bite them on the skin like the others? It's not like it would crawl out and back into the bowl to be eaten by the other person.
Other mistake: Irv and Blaire's death scene doesn't make sense. When Irv poured butter on the popcorn, he should've noticed the spider in the bowl. Also, when Blaire picked the spider up, she should've felt it. Both of them still appeared to be watching the TV after being bitten, which also didn't make sense. Why didn't they have seizures like the other victims?