Continuity mistake: When Becky is in the shower, the position of her hair as she washes it changes, and the amount of shampoo bubbles in her hair differs also. (01:09:10)
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. (01:18:15)
Continuity mistake: When the General jumps out of the flames, one of his legs breaks off after he hits the ground. All eight legs are intact after he is blasted by the nail gun and crashes into his nest.
Continuity mistake: When they perform the autopsy on the three victims, Metcalf is all grey and stiff, whereas the two exhumed victims look alive and fresh.
Continuity mistake: Near the beginning, the clumsy guy walks backwards into a giant cobweb, so he is covered in it, but, as he leaves, there isn't a cobweb in sight on him.
Continuity mistake: When Jerry Manley is shown in the coffin his head is on the right side. When they show the shot inside the hole before inserting the poles, his head is on the left.
Continuity mistake: It's way obvious that the king spider attacking the doc at the end is animatronic or CGI as it's appearance changes. In the far shots the legs are wide spread and it's a purplish color. But in the closeups it's black and half the size.
Continuity mistake: After Becky's dad comes into the bathroom, and she screams, covering herself with the shower curtain, you can see her brother, who had died at the football game considerably earlier in the movie, through the bathroom's doorway, standing in the hall. It's only for a split-second, but as long as you're looking in the right spot, it's very clear.
Suggested correction: Not that what you said is wrong, but it actually makes sense. Metcalf was bitten by the original, non-bred spider. The other victims were bitten by spiders that were part house spider, part deadly spider. Therefore, the effects of the bites were different. I'm quite glad that I only had to see one gray, shriveled-up body.
Actually all three were bitten by hybrids.