Factual error: At the climax of the movie, Alice swings the machete at Mrs. Voorhees and decapitates her. When the blade makes contact with Mrs. Voorhees' neck, her head flies off at an incorrect angle, as though the cut began on the opposite side.
Revealing mistake: When Ned is pretending to drown, Brenda swims out to rescue him. You can see that she and Ned stay underwater for a few seconds, until their cue to emerge. (00:23:30)
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)
Audio problem: In the beginning, Claudette and the other counsellors are all singing. When they get closer you can see that Claudette is playing the guitar, then she stops, but the guitar playing and singing still continues. (00:02:10)
Continuity mistake: After Brenda hears a noise, she puts her book down next to the candle, and walks to the door. When she gets to the door, the book is now by the opposite side of the candle. (00:52:50)
Revealing mistake: When Steve Christy is leaving the diner, it shows the outside of the diner, where it is raining. It's very obvious that the "rain" is just a sprinkler.
Visible crew/equipment: When Mrs. Vorhees throws Alice onto a table you can see a mattress under it catching her fall. (01:18:35)
Revealing mistake: When Alice finds Bill killed and hung up on the door you can see Bill blink his eye. (01:08:05)
Continuity mistake: After Brenda is thrown through the window, she is facing to her right. Later when Alice goes back to the kitchen, she is facing to her left. The glass and wood around her changes too. (01:11:20 - 01:20:15)
Continuity mistake: When the kids are at the beach, Brenda shows up saying "Hey you guys. Ready to get back to work?", while placing her foot on a red towel. When it cuts the towel has changed position. (00:23:00)
Visible crew/equipment: In the scene at the diner after the kids have played "Strip Monopoly" there is a shot of Sandy behind the counter and some customers walking out of the diner. Look behind the last woman walking out and you can see a crew member reflected in the window. (00:46:25)
Audio problem: When the kid is playing classic guitar the movement on the guitar's neck doesn't match the music. He somehow manage to play high tones on low frets. (00:36:45)
Continuity mistake: When Annie talks to the dog, its position changes between shots. (00:07:00)
Continuity mistake: In the scene when Alice decapitates Mrs. Voorhees and Mrs. Voorhees raises her hands and grabs air, if you look carefully, the hands have hair on the back, even when, during the chase scenes, she doesn't have hair on the back of her hands. (01:27:55)
Visible crew/equipment: When Pamela Vorhees pulls over to pick up Annie we can see a man's arm reflected in the front shield sitting in the passenger seat. (00:18:30)
Continuity mistake: After Alice bangs at the lock with the end of the gun, the position of the lock and it's chains differs through the following consecutive shots. (01:17:50)
Revealing mistake: When Jack and the kids get up to the cabin you see Steve chopping on a stub in order to remove it. He then gets help from the kids to tip it over but there are no chop marks on it. (00:13:20)
Continuity mistake: At the lake when they pull the floating object by the pier the girl on the right side is about ten feet ahead of the object. When it cuts she is behind it. (00:21:35)
Revealing mistake: Toothpicks visible after Alice cuts off Mrs. Voorhees' head. (01:28:10)
Continuity mistake: When Alice runs into the barn to hide from Pam, as she slides the door open, a plank of wood falls over, to the right of the door. In another shot of the barn, it is upright again. (01:17:00)
Chosen answer: Just after the credits, there's a bank sign that says "Friday, 13 - 7:01 - 60 Degrees". Then the DJ says "It's 7:01 on Friday the 13th of June." and goes on to say some more about it and lists some other bad luck superstitions. At two other points in the movie, two characters (Ralph and Tierney) say "it's Friday the 13th". So there are at least four references to the fact that the movie takes place on Friday the 13th.
Myridon