Visible crew/equipment: A boom mic is visible at the top of the screen in one of the alternate endings where a mortician comes to get the body of Billy from the coroner.
Continuity mistake: At the end, while Billy chases Kelli, Kelli knocks over a cart of surgery supplies, spilling the material forward. However, a few shots later, Billy is shown picking a scalpel up from the small tin pale, which slid ahead of Kelli. So how could Billy have picked up the scalpel if he was behind Kelli?
Answer: Billy's mom is insane and does not possess a fully rational mind.