Visible crew/equipment: When Annie jumps from Mrs. Voorhees' jeep, a white elbow pad can be clearly seen on her right elbow. (00:20:00)
Visible crew/equipment: After they've killed the snake, Alice says "Is it dead?" and as the camera pans up, the boom mic's shadow is visible moving across the wall, directly over Ned's head and the red box. (00:26:05)
Visible crew/equipment: When Annie goes into the shop to ask where Camp Crystal Lake is, you can clearly see the reflection of a boom mic in the window, above the head of the cleaner. (00:07:40)
Continuity mistake: When Annie goes over to the dog and stops to talk to it, in the first shot the dog is in the sun, yet in the next shot it is completely shaded. (00:06:50)
Answer: 1. She was most likely hanged. 2. Mrs. Voorhees wasn't possessed by Jason. She simply went insane when Jason drowned and wanted revenge. 3. He's not burnt, only disfigured.