Revealing mistake: When the scientists inject the mouse with poison, they put it in a jar. The, after they place it down you can see someone's hand swap the jar for one containing a dead mouse. You can even hear it.
Revealing mistake: When Becky sees the spider in the shower, there are two instances when you can see the bodystocking she's wearing, covering her breasts, to preserve her modesty, most noticeable when she screams.
Revealing mistake: In the scene where Dr. Ross Jennings is trapped in the corner of the cellar, you can see that the tarantula which starts climbing up his leg has a huge black stick stuck to the back of its body, pushing it along.
Continuity mistake: When Irv and Blaire are snuggled up on the couch, watching Wheel of Fortune, watch the big bowl of buttery popcorn they have. In the first shot it is full to the brim. In the next shot it's half full.