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)
Continuity mistake: The trees and scenery around and behind the truck, as we first see Ned, Bill and Marcie, changes bewteen closeups and wideshots. (00:12:00)
Continuity mistake: When Alice runs to the beach, there is only one canoe sitting there. But when she finally gets in the canoe and pushes off, there are two. (01:23:10 - 01:25:15)
Continuity mistake: After the sheriff gets the call over his radio, he turns on his red lights. In the next shot they are off again, and are then turned on once again. (01:00:25)
Continuity mistake: First Bill and Alice are looking under the bed for the snake. In the next shot Alice is not the one looking under the bed, but she is kneeling behind Marcie, who now is looking under the bed with Bill. (00:25:35)
Continuity mistake: When they see the snake in the cabin they all jumps after it under the bed in panic. But in the next shot from under the bed you see them calmly lifting the sheet on the bed to look under it. (00:25:25)
Continuity mistake: When Steve's car won't start you see a police car pull over. The sheriff turns on its red lights and Steve goes towards it and opens the door. In the next shot you see him talking to the sheriff, but now the lights are off, it cuts again and the lights are on. (00:50:30)
Continuity mistake: When Annie gets into the bar and asks about Camp Crystal Lake, you can see the woman behind the counter standing leaning in at the end of it. Then two cuts later she turns around, suddenly standing by the cashier. (00:07:40)
Continuity mistake: Just before Annie jumps out of the van, the truck is turning a bend. When the truck stops and backs up, the road is straight. It's a clearly new road. Also, the trees and leaves along the ditch have changed. (00:19:55)
Continuity mistake: When Alice runs to the lake to Bill she says "Bill, Steve wants to know if you need more paint", while holding her arm to her hip. When it cuts her arm is down. (00:16:20)
Continuity mistake: When Ned fakes drowning he is a decent distance from the dock. When he is rescued he is much closer.
Continuity mistake: When Alice wakes up she has white socks on. When she walks to the kitchen they are black. (01:08:00)
Continuity mistake: Crazy Ralph comes out of the pantry and Alice screams. Marcy and Ned come running into the kitchen. Ned is eating a hamburger that hasn't been cooked until the next scene.
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.