Friday the 13th (1980)

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.

Plot hole: When Brenda is thrown out the window, Alice immediately runs outside to see Mrs. Vorhees pull up in the jeep. How can this be if she just threw Brenda in the cabin?

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)

Hamster

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)

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)

Hamster

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)

Hamster

Continuity mistake: When Alice opens the pantry door to find Crazy Ralph in there, you can see Ned and Marcy running to the kitchen. It cuts to Ralph, then back again and the other two run into the kitchen again. (00:28:55)

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)

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.

Continuity mistake: When Annie talks to the dog, its position changes between shots. (00:07:00)

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)

Mortug

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)

Mortug

Visible crew/equipment: When Mrs. Vorhees throws Alice onto a table you can see a mattress under it catching her fall. (01:18:35)

Mortug

Continuity mistake: When the kids are at the beach, Alice 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)

Mortug

Revealing mistake: When Alice finds Bill killed and hung up on the door you can see Bill blink his eye. (01:08:05)

Mortug

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)

Hamster

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)

Mortug

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)

Hamster

Visible crew/equipment: After they've killed the snake and Alice says "Is it dead?" the boom mike shadow is visible moving over the door behind her. (00:26:05)

Mortug

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)

Mortug