When Eric goes to check on Olivia, he walks into the room and looks toward the bathroom door. As you can see the door knob is on the right side of the door, but when he goes to open the door, Camera shot from the floor, the door knob is on the left.
After Mia crashes the car into the pond, the car has its footwells full of water. The doors are above the water line and at such an angle that it could not flood as shown. The car's depth in the pond is also inconsistent with the area immediately around the car; Mia exits the car and into the water at a depth near her waist.
When arriving at the cabin Mia is complaining about a really bad smell, which the others only recognize after the cellar door is opened. But since the floor is made out of wooden plates with visible gaps between then, the smell should have been noticed by everybody from the beginning.
After Eric is stabbed in the eye several times and pulls out the needle from under his eye, in the following scene the mark from the needle is lower on his face than where he pulled the needle out from.