When the blood falls on Carrie, it really only hits the left side of her hair and her shoulders. In following shots, she is soaked in blood.
There are several signs posted about the time of the prom, all of which say from 9 -1. (One says 9-1 p.m., which, of course, is incorrect.) Sue Snell asks the time at the family dinner on the night of the prom and is told that it is 8 o'clock. Shots immediately before and after the dinner scene show the prom going in full swing, even though it is not scheduled to start for another hour. Additionally, it would still be light outside on May 25th at 8 pm.
After Carrie is covered in blood, her crown disappears between shots.
Norma P.J. Soles) has her hair styled at the salon in preparation for the prom. Immediately afterward, she is back at the gym setting up things with her hair in braids and wearing her baseball cap.
When Miss Collins begins calling the roll, the first shot reveals a girl dressed in dark blue sitting among several girls higher on the bleachers. In the next shot, she's sitting in the front row next to Helen. But in the shot after that, she's in her original place.
The bucket of blood that is dropped on Carrie at the the prom would be significantly darker, having oxidized from the time it was collected.
At the beginning of the movie, the far side volleyball team has six players (one is Carrie (Sissy Spacek)) and the near side team has seven players plus an additional player serving (out of camera range).
When Carrie's upstairs breaking her mirror, the scene switches to Margaret White downstairs at the sewing machine. She is sewing a black dress, but the thread loaded on the sewing machine is bright red.
When the girls are serving Ms. Collins' detention on the athletic field, part of their exercises is doing sit-ups, but they are doing them incorrectly with their legs straight. It is important to do sit-ups with the knees bent to avoid pain and stress on the lower back.
When Carrie tells Margaret about the prom, she throws her drink in Carrie's face. This snuffs out two of the candles and significantly darkens the room. A few seconds later, Margaret stands up and the kitchen light behind her is suddenly turned on, lighting up the room.
In the opening shower scene, all the girls who are toweling their hair dry have obviously dry and permed hair and are just going through the motions. Also, the girls who do have wet hair before during the opening credits suddenly all have dry and nicely styled hair when Carrie starts to panic.
When Carrie (Sissy Spacek) looks out her window, when she hears a horn honk, you can see the spike mark where Tommy's (William Katt) car is supposed to stop.
During the dream scene at the end, a red Volkswagen Beetle is seen driving down the street backwards, giving away the fact that it was shot in reverse.
When Chris and Billy are in the car, Chris calls Billy a stupid shit and he slaps her cheek with the back of his hand. A loud sound is heard, but he clearly isn't actually hitting her hard.
The story takes place during several days leading up to prom, yet Norma is clearly seen wearing the same outfit and baseball cap in every single scene except for gym class and prom.
Chris (Nancy Allen) is somehow able to give her boyfriend a blow job and talk to him at the same time without her voice being distorted in the least.
At the Prom the keyboard player slides his hand from right to left on the piano but the audio goes from low to high (opposite) during the song.
Just before Miss Collins slaps Chris, it's clear from Chris's mouth movements that she says, "Stick them up your ass," but the last word is not heard on the soundtrack.
After the bucket of pig's blood falls, you hear the 'blood' spilling long after the bucket has emptied.
Camera shadows are briefly visible on the prom guests.
Chris is trying to convince Billy to help her prank Carrie at the same time that Sue is trying to convince Tommy to take Carrie to the prom. At this point, Chris has no way of knowing that Carrie is going to be at the prom at all.
It is completely implausible that Carrie can be so ignorant of menstruation simply because with the locker room is set up as it is (open w open showers), with a machine to dispense sanitary products, there is no possible way that in 4 years of using this locker room (Carrie is a Senior), she would NEVER have heard a single girl mention periods or sanitary products, given the chattiness of the crowd in the locker room scene.
When Ms. Collins is calling the role in the gym, she walks over to one of the girls and snaps "Katie!" But the character's name is Helen.
There are a number of girls standing behind Helen and the teacher could have been speaking to any one of them. Helen could have reacted simply because the teacher was standing right in front of her when she snaps out 'Katie!'