Jack claimed he wore no underwear, yet a while later, in his sexual encounter with Krista, he is clearly wearing underwear.
When the girls come back to the hotel room to kill Jack, the plastic they used to suffocate him was pulled up over half his face, yet in the next scene, the plastic is fully covering his face.
The date and setting was late December in Utah, but the weather seemed unseasonably warm.
When Jack brings Melinda to the hotel room where all the girls are tired up, Jack hits her in the face and she is bleeding from the right side of her mouth. However, when the girls escape and then come back to kill Jack, there is no blood on her face and it doesn't even look like she was hit at all.