Oxycontin makes your pupils constrict, not dilate. It is said twice about the opiate addict.
Movie referred to skin-walkers as just native American werewolves, skin-walkers don't just turn into wolves and it's not involuntary, skin-walkers are said to be able to turn into almost any animal when they chose to, they also are known to have the ability to mimic voices to lure in people.