In the opening sequence, Tony walks down the street and it's visibly sunny and the pavement is dry. Then when he runs across the street toward the paint store, the street and sidewalk are wet from rain.
On the first disco night, there is a shot of a bar, which we see a dancing women, bartender, three men sitting at the bar, and another man at the bar wearing a tan suit, he is reflected in the mirror behind the dancing lady. These same people are shown in the same place on the second disco night, both nights when we see them the song "If I Can't Have You" is being played.
After Tony walks outside with Joey and his girlfriend to the car in which Double J is using with a lady friend, Tony walks away back into the disco leaving Joey and his girlfriend long behind him. When the next shot opens and Tony walks back into the disco to do the line dance, Joey is dancing with Annette in the background of the same shot and then they all come together to dance.
At the final bridge scene when Bobby C is climbing up the cables of the bridge, he has on white sneakers. Moments later when he's talking to Tony on bridge's beam he does a headstand and he has on black shoes.
Upon entering the discotheque in the beginning of the movie, Tony greets the same man (in blue shirt) twice.
When Stephanie and Tony are dancing at the dance studio the first night they get together to practice there are advertisements and decorations on the wall for Valentine's Day. When the scene cuts to later in the evening when Tony and Stephanie are walking home the storefronts have decorations and sales fliers for Easter week.
The song "Stayin' Alive" by The Bee Gees is misidentified as "Staying Alive" in the opening credits sequence.
When Bobby hangs from the vertical suspenders on the Verrazano-Narrows Bridge, they wiggle quite visibly, indicating that they are made of some type of rope as opposed to the steel found in the cables of most suspension bridges.
When Double J crashes Bobby's car through the Barracudas hangout, you can see obvious dummies sitting in the car as the impact shot is slowed down.
When Tony and Stephanie go to dance to Tavares' version of "More Than a Woman", Tony places the needle on the record, and the arm skips all the way to the end, revealing that the record player is broken and the music dubbed in later.
When Bobby asks Frank (the former priest) about getting a papal dispensation for an abortion, the camera angle changes so that the side of Bobby's face is shown and all of Frank's can be seen. Frank answers Bobby and then Bobby says "Well maybe you can, maybe you could do it for me." At this point, Bobby's mouth is clearly not moving except once, which indicates that his retort was dubbed in over a one word retort.
(at around 1 min) In the first scene that Tony gets picked up by the boys in front of the candy store to head to the disco, it is clearly seen that the driver of the '64 Impala is in fact a stuntman instead of Bobby C, whose voice is dubbed in and then appears as the driver in the interior car shots.
When Tony is first picked up in the Impala, as the boys review their inventory of pills and alcohol, the camera rigging can be easily seen reflected in the passenger window where Tony sits, especially as a lighted "TRAVEL" sign passes by.
Reflected in the mirror in the studio as Tony and Stephanie are practicing their "More Than a Woman" routine.
When Tony is walking with Bobby C. by the paint store, a crowd of people watching the scene being filmed is reflected in the last window they pass before they reach the corner.
Camera shadows in some scenes, such as on the group's car.
Just before Tony gets off the subway train the first time, "45th Street" station signs are visible from inside the car. After he's gotten off the train, he is waiting for a train at "53rd Street". Neither station is a transfer point in the NY subway.
When Tony interrupts a dance class to ask the instructor about Stephanie, you can see the boom mic reflected in the mirror towards the right.
When Father Frank Jr. is leaving the Manero house, when Tony, Father Frank Jr. and the driver load the bags into the car, a boom mic shadow is visible on the top portion of the car.
When Frank Jr. leaves the family home, as Tony and Frank Jr. approach the car door, the shadow of the boom mic is visible on the tree trunk.
When Tony talks with Stephanie in her apartment after the "lonesome subway ride" scene.
When Tony is walking with Stephanie to get coffee you can hear a girl scream. This is because there was a group of girls watching them film the scene and they would scream when they saw John Travolta.
The sign on the roof of the 2001 Odyssey disco misspells the word "Odyssey" as "Oddyssey," although the vertical sign attached to the building wall spells the word correctly.
Tony is telling Stephanie about how a worker died during the making of the Verrazano Bridge by falling into the concrete. While that's a popular myth, it never actually happened.