Continuity mistake: In the scene where Jessica is in the shower crying and the power goes out, she gets out, puts on a white t-shirt and goes walking around the house. When she walks through the garage door and grabs a hammer, there is blood on the front of the t-shirt (right at or a little lower than her waist and looks like someone grabbed the shirt with a bloody hand). Where did it come from? She didn't run into anything or anyone. [There's a deleted scene showing her step on a piece of glass. She gets blood on her hands when she pulls the glass out, then presumably wipes her hands on her shirt. Still a mistake, as removing that scene means the blood appears from nowhere, but there's the reason.]
Continuity mistake: There are two times after the female FBI agent gets out of the shower that she is wearing underwear when she put none on, and the pair that she has on is completely different from the one she originally took off. The first is when she runs directly to the door from the shower after the power goes out. The second is seen when she puts on only a towel shortly after, and then falls over the railing, you can see she's wearing underwear there as well. (00:04:45)
Continuity mistake: At the start of the film Jason chases Agent Marcus from the cabin, and she is barefoot. But in the shots of her running through the woods, in some shots she is barefoot, in others she has white socks and big black boots on, and in others she has flesh-coloured trainers on. (00:05:10)Hamster
Continuity mistake: The note that Jessica found in Stephanie's crib changes. When she finds it, it reads "I have what you want " and is written in blue ballpoint pen. But when Steven finds the note later, it reads "I have your baby " and is now written in thick, black permanent marker. (01:08:35 - 01:11:15)Hamster
Continuity mistake: When Robert, who is possessed by Jason, is reaching through the car window to get Jessica and Steven, you can see his reflection on the car hood. This reflection should show Jason, as we've already seen in the movie that the host body Jason is in should show Jason in any reflection. (01:00:50)
Continuity mistake: After the female FBI agent falls over the railing and through the coffee table, the two legs closest to the screen roll away, but when the table is shown again, the legs are underneath it. (00:04:50)
Continuity mistake: The father of Jessica's baby, while in jail, had some of his fingers broken by Craitan Duke, but in the next scene, he is fighting another character and his hand with broken fingers is working fine.