When Marie sees, then steals, the keys on Dr.Rose's desk they have only one key on the bunny key chain. When she shows the keys to Vincent afterwards there are several keys on the key chain. When Alex later throws the keys in the lake there seems to be only 2 keys on the chain.
Marie's joint is in/out of her mouth in different camera angles during the first pot smoking scene.
When hot-wiring the car, he crosses the wires but the engine sound only starts after he strikes them together (as if sparking to light a fire) and continues multiple revolutions after the wires are no longer touching. In reality, the starter will only engage and revolve (thus the engine starting sound) while the wires are still in contact.
When Marie and Robert kidnap Alex the full crew can be seen in the reflection of the glass windows and doors.
At around 0:10:45, Alex touches his face with the gloves on, a person with OCD with Alex's characteristics would never touch his face with gloves that has been in contact with non clean objects.