Visible crew/equipment: When Julie says "It's probably just your nerves" then Heather replies "Nerves?!", above Heather's head you see a boom mic dip down into view. (00:12:25)
Visible crew/equipment: When Heather is leaving to go to her TV show, she and Julie walk out Heather's house. As they walk out and talk, you can see a boom mic dip down into view for a while. (Seen on DVD version) (00:13:25)
Visible crew/equipment: When on the phone to Chase, Heather says "He's had some sort of an ... episode" and as she says this a boom mic briefly dips into view, above her head. (Seen on DVD version) (00:23:40)
Visible crew/equipment: The boom mic dips into view once again whilst Heather is on the phone to Chase, as she says "...Like Freddy." (Seen on DVD version) (00:24:00)
Visible crew/equipment: The boom operator for this film should have been fired. You can the microphone dip into view whilst Dr. Heffner is whispering to her junior nurses, as you can hear Heather wrestling with the security officers. (Some DVD versions.) (01:14:00)
Visible crew/equipment: After Julie is killed, she falls to the floor, and if you look closely you can see the big black mattress she lands on. (Seen on DVD version.) (01:18:35)
Visible crew/equipment: In the playground scene, when Dylan jumps from the top of the rocket, it's an adult stunt double.
Chosen answer: Mostly just very subtle hints. In the beginning when she arrives right around the same time that Heather gets a call from the psycho-stalker, suggesting a possible connection. And the fact she's alone with Dylan many times during the film, as she could be subtly manipulating him to act out.