Revealing mistake: In the soda shop, the waitress turns off the lights with her elbow because her hands are full, but she misses the light switch by 6 inches.
Audio problem: During "We Go Together" at the end, John Travolta's mouth is not in sync with the words "we'll always be like one." He appears to start singing "that's the way it should be" before realizing and correcting his mistake.
Continuity mistake: At Frenchie's sleepover when they are talking about piercing Sandy's ears, it shows Sandy holding the wine bottle and passing it to Jan. Then it cuts back to Sandy and she is still holding the wine, then it cuts back to Jan and she has the wine again.
Revealing mistake: At the dance, there's a scene where everyone started dancing after Cha-Cha and Danny won the trophy. Well Marty comes in from the side of the screen and lands on the floor in some kind of split, and you can see she is wearing a knee pad on her right knee.
Continuity mistake: When "Crater Face" comes to the dance with Marty and Rizzo, he takes his sunglasses off twice.
Continuity mistake: In the scene where the whole gang is eating at the soda shop, everybody starts leaving. Doody is in the back, in the middle, on the railing. He's getting ready to leave, takes a bite of his ice cream and sets it down. In the next shot, he sets it down again.
Continuity mistake: In "We go together" they all dance forwards. When the camera changes angle Frenchy and Doody have switched sides.
Visible crew/equipment: In the soda shop scene where Sandy and Danny are at the jukebox, the reflection of the boom mic is clearly visible in the chrome part of the jukebox. [True of videos and early DVD releases - in later DVD releases the reflection has been removed].
Continuity mistake: In the middle of the dance contest, Patty Simcox does a funny front walkover, and comes dancing towards the camera. Over her shoulder, you can see Sonny running up behind her. But suddenly it cuts to another angle, and Kenickie is running up behind her to lift up her dress, and Sonny is nowhere to be seen.
Factual error: When the Pink Ladies are walking Sandy into the outdoor cafeteria, just after she tells them the name of the boy she met last summer, all the cars in the background are from the 70's, not from the late 50's or early 60's. This actually happens twice in the same scene.
Continuity mistake: Sandy walks over to meet the girls after doing a cartwheel. On Sandy's cheerleading uniform, there is a LONG red string right next to the letter on her shirt. Then, suddenly, the string disappears in the very next shot. Then in the scene after that it is back again, and then the string is back on her shirt.
Audio problem: At the cotton candy stand at the graduation carnival, Blanche is seen silently mouthing the question "How many?". In the next scene, from a different camera angle, the same question is asked - this time with audio intact.
Continuity mistake: During the slumber party at Frenchie's, when Rizzo brings out the wine, check out the junk on the headboard. Later in the scene when Marty is putting on her robe, the headboard is clear and now has a black fan on the left. Then even later when Jan says "You ain't getting your hands on my ears" the headboard is cluttered again, with the black fan too.
Continuity mistake: When the three T-Birds go to moon at the TV camera at the National Dance Off, Doody says "1, 2, 3, go!" and pulls down his trousers to his ankles. In the next scene, his trousers are suddenly pulled right up to his buttocks.
Revealing mistake: When Sandy checks into school for the first time, she goes down to the office and the assistant principal gives her some forms to fill out. If you look closely, you'll be able to see that the top form is just a blank piece of paper.
Factual error: At the graduation carnival at the end of the movie, Danny enters wearing a letterman's sweater and explains to his buddies that he earned it by lettering in track. However, on his left sleeve are two stripes, indicating that he lettered in two separate years. Since you are only awarded a stripe for each year you letter, and since Danny was a senior when he lettered in track, his Rydell letterman's sweater should have had only one red stripe on his left arm.
Continuity mistake: After Danny has danced around the car with the saran wrap he is shown spinning around numerous times, and then stops with his back to the camera. However, in the very next shot, his arms are suddenly up in a pose far too quickly for him to have done in the time alloted.
Continuity mistake: There is a scene in which Danny falls over a hurdle. If you watch his falling frame by frame you will notice that only his right leg is stretched first. Then the camera angle changes and suddenly his left leg is stretched, while the right one is bent.
Continuity mistake: During the dance off, Sandy and Danny are dancing in the center and everyone is watching them. Behind Sandy, Cha Cha walks out and puts her hands on her hips. Then, the camera does a close up of her doing this. So she actually walked out twice.
Character mistake: When Frenchie is the only person remaining in the soda shop a guardian comes on and starts singing a song. While he is singing the song (toward the end of his singing) all the girls scatteringly head back toward the stairs. While they are walking up, one of the girls trips over her high heels. It is clearly shown, she's toward the front going around the back of the seat Frenchie is sitting in, around the round thing.
Revealing mistake: When Sandy is at the shop with the jock, then she goes to the jukebox, the picture behind the jock is all blurred out. You can tell it is a Coke sign - Coca Cola cancelled their sponsorship after filming.
Continuity mistake: After Danny has knocked over a hurdle, we see him getting up; however, the Hurdle has either moved and stood itself back up or it's disappeared completely. In the next shot it has returned to its fallen position.
Continuity mistake: When the students are dancing to "Hound Dog" at the National Dance Off, they go up to the TV camera and start waving. You can see in the crowd a girl in a blue dress jumping up and down, but when we see it on the TV from the Frosty Palace, the girl is nowhere to be seen.
Other mistake: This mistake occurs during the dance sequence 'You're the One that I Want.' John Travolta and Olivia Newton-John have just emerged from a 'Shake Shack' and are now ascending a ramp. For the lyrics ,Hoo hoo hoo... honey,' the camera zooms in close to their faces. You can see that the dance move is for the two actors to bob their heads close to each other's so that they nearly touch. They do it right the first time, but the second time they visibly mess up. John Travolta seems to try to fix his mistake, but Olivia Newton-John appears to crack up and leave the frame.
Factual error: In the scene where Danny is talking to Sandy at the Frosty Palace, the jukebox behind them is a 1973 model, but the film takes place in 1959.
Continuity mistake: Sonny has a lunch bag in his hands when they arrive at school. After they see and talk with Zucco, the bell rings and they head for class. As they start leaving, Sonny doesn't have his lunch bag anymore.