Revealing mistake: Despite her very vigorous thrusting when she makes love with Paul, the bed sheet covering Marcy's ass doesn't get shaken off. Not even a little bit. Also, when they finish, she collapses on to him and he wraps his arm around her back. When he does this you can see that his arm is coming up from near the bottom of her waist. If his arm lines up with her lower waist, then Marcy's crotch must line up with his chest or belly - much higher then it needed to be to have sex.
Revealing mistake: As Marcy is running away from the mad dog, there are a few instances when we can see the sleeve of a white top inside her bathrobe. She was supposed to have just run out of the shower in a panic, so throwing on a top and then a bathrobe doesn't seem like something she really would've done.