When the guy is in the MRI and is freaking out, the guy he was playing chess with was in the room with the nurse. The nurse then asks him to calm the guy down, and he goes in the room with the MRI. There are two goofs here! First, he would not have been allowed to be in the room with the nurse. Not being family, he would have been stuck in the waiting room. Second, if he were allowed in the room with the nurse, he would not be allowed in the room with the MRI machine while it was being used! No one but the patient is allowed in the room while the machine is running.
When Stacie is locked in the bathroom the ants seem to invade from a vent near the floor, but one bottom shot reveals that they are cgi-ed, appearing downwards a line that extends over the vent and the surrounding wall.