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.
Other mistake: In the opening animated sequence, it shows Rizzo taking off a top and her neck stretching. She looks in the mirror. As she is facing the mirror you can see that even with the elongated neck you still should be able to see her face in the mirror, but the elongated reflection just shows the neck looking much longer than it really should. Also, as the animation goes on you see Riz turning sideways but the reflection in the mirror does not match. She is sideways while her boobs in the reflection are facing the other direction. Then when she puts the black blouse on her back is to the mirror but we see her front in the mirror.