When Nina is at the dinner table, you see the mutants put the food on her plate, then after she throws up, you can see that the plate is clean.
When Kimberly Caldwell calls her agent he complains that it's 4am in Los Angeles. She's driving in West Virginia, and the shadow the car casts indicates the sun is directly overhead, so it's about midday (the shadow sits under the car in every shot). However, if it's 4am in LA, it should be 7am in West Virginia, so the sun should cast long shadows.
When Kimberly is cut into half, only her intestine comes out not her blood.
In the scene where two people are shot with one arrow, the arrow is obviously fake, as the tail feather portion does not line up with the middle portion.
When Rorelee Tio (Sister) drives the old truck you can see her
arm and hand really clean and delicate despite the filth of the character.
When Elena tries to run from the hillbillies she's struggling with her shorts, but when she falls in to the river they are fully on.
When Dale is shot with the first arrow the entry and exit sides are not continuous. The feather side is higher than the tip side.
It is established when her character is introduced that Amber was in the Marines. Later, another character says he read about her and her time at West Point. A Marine would not have attended West Point, that is only for US Army officers. A Marine would have attended the US Naval Academy.