During the first dance in the gymnasium ("Rock and Roll is Here to Stay") when Danny and Sandy are dancing near the end of the song, there is a scoreboard visible very briefly which reads either "Presented by class of 1971" or "Presented by class of 1974", far later than the time when the story takes place.
After Cha Cha brings down her scarf to start the car race on Thunder Road, an Amtrak train can be seen above the concrete riverbank at the left of the screen. The F40 locomotive and Amfleet passenger cars of the train began service in the mid 1970s.
"Rama Lama Ding Dong", a song referenced in the lyrics of "We Go Together" , sung throughout both the show and film version, did not surface until the summer of 1961, when it became a million seller for "The Edsels".
In the final sequence while singing "You're the One That I Want," Danny and Sandy spin twice in the amusement park walkthrough (The Shake Shack). On the second twirl, you can tell that it is not perfectly in sync with the music.
In the beginning of "You're the One that I want" Danny Zuko falls down in the dirt and when he gets up his black shirt is dirty in the belly area. Also, Olivia Newton-John's character puts her dusty shoe on his shirt as well. Several scenes later, his shirt is clean again and remains clean for the rest of the song.
In the closing number, "We Go Together," Doody and Frenchy switch places between the lines, "When we go out at night/And stars are shining bright." Also, the blonde guy to the left of them goes from a sitting position to a standing position in the same error.
A dummy is being burned in effigy during the pep rally; however, the amount of flames on the dummy goes from small to large (the dummy is fully ablaze) then back to small (a closeup shows the fire only on the upper torso and one can still read the undamaged sign on the dummy).
At the start of the 'National Bandstand' dance-off (the "Born to Hand Jive" number), the head of the cowboy decoration in the gym tips forward, spilling wads of paper off the brim of its hat. However, in the establishing shots prior to that there is no paper on the hat brim. In addition, a few seconds later, and as seen in other shots that follow, the head is intact and back in proper position.
During the dance scene, when the teachers are congratulating Patty and Eugene, Eugene starts waving to the students. In the next shot, when the camera is facing the stage, he and all the other students are standing still.
While in the shake shack, some of the close-ups do not match the other scenes, in the far shots there are people and trees behind the bars, in the close-ups there are neither, and also the wall colors are different between shots.
In the dance-off, just before Cha-Cha replaces Sandy as Danny's dancing partner, there is a wide shot of Danny and Sandy dancing. In the corner you can see Cha-Cha walk out from behind some students. The camera then makes a close-up and she repeats the same movement.
During the fast dancing, there is bright daylight coming in through the gym windows. Seconds later, they turn down the lights for the "Blue Moon" slow dance. The gym is totally dark. This would be impossible since there was daylight coming in through the windows seconds ago.
All of the actors are far past the typical high school age of 14 to 18 years and do not accurately represent high-school aged children: John Travolta (Danny) was 23 years old at the time of shooting; Stockard Channing (Rizzo) was 33 years old; Olivia Newton-John (Sandy) was 29 years old; Both Barry Pearl (Doody) and Jeff Conaway (Kenickie) were 27 years old; Michael Tucci (Sonny) was 31; Kelly Ward (Putzie), at 21 years old, was the youngest of the bunch, while Didi Conn (Frenchy) was 26 years old at the time of filming.