In the closing driving scene both of Emily's hands can be seen on the steering wheel multiple times from the behind shots, whereas in the face-on shots she's shown to be clearly only driving with one hand on the wheel whilst she holds the oxygen mask.
Emily stands on something at the water's edge. When the camera looks along the beach there are Cornish pasty creatures all along the shoreline, but from the very next camera angle there are none.
Emily sees something in a house that she doesn't like so she leaves the room and locks the door behind her. For safety reasons, rooms can never have a lock on the outside only. This is to stop people being accidentally trapped inside.
When Emily is testing the scuba equipment first time, she is holding the regulator upside down. Before there has been revealed that she is a certified scuba diver so it would be highly unlikely. Afterwards she uses her regulator correctly.