Continuity mistake: In the prologue of the movie, two guys on the Sharks throw yellow paint on Baby John, Arab, Action, and Snowboy. When they are talking to Lt. Shrank and Officer Krupke, they are all clean, but wearing the same clothes as earlier. (00:13:05)
Continuity mistake: When the gangs are fighting in the playground, in the aerial shot you see that two of the seesaws are pointing up away from the gangs. When the Jets leave a few minutes later, all of the seesaws are pointing up away from where they were originally. (00:14:16 - 00:17:39)
Continuity mistake: In the "Dance at the Gym" scene, while everyone is doing a pelvic swivel with their partners, Riff's arm is around Graziella's waist. In the next shot, his arm is down. (00:32:30)
Continuity mistake: At the dance, when everyone is swaying with their partner, you can see both of Ice's hands on Velma's back, then in the next shot when it's following baby John, you can see Ice put his hands on her back again. (00:32:30)
Revealing mistake: In the dance scene, when the two gangs are "battling," if you look in the background at the Sharks side, you can see Maria among others mouthing the rhythms of the songs. (00:37:25)
Other mistake: When Anita sings, "and the natives steaming" her fingers get caught in the fringe of her dress. (00:50:05)
Audio problem: When the sharks are singing "We're going to hand them a surprise tonight" in the quintet version of Tonight, someone sings the wrong note on the word "Tonight". (01:33:20)
Continuity mistake: Maria prays that her brother's death is untrue, she says "Le suplico no puede ser." Her fingers are woven between each other. When they show the back shot of her, her hands are cupped and then she goes back to the previously mentioned position. (01:48:05)
Continuity mistake: When Maria is hitting Tony while saying "Killer," her hair is across her left cheek. In the next shot, it is completely away from her face. (01:48:20)
Other mistake: During "Cool," Baby John spins around and when he stops with his arms spread out, his right foot stumbles a little. (01:58:15)
Other mistake: During "Cool," there's a shot where they're doing a sort of knee turn, and you can see Tucker Smith in the background spinning too many times (you can see him start to stick out his arms to stop himself). (01:58:20)
Continuity mistake: Toward the end of the movie when Doc slaps Tony, Tony grabs his face. Then they show a behind shot of Tony and you can see his hand moving slowly away from his face. But when they show a front shot of Tony his hand is back on his face. (02:16:45)
Revealing mistake: In the final scene, if you look in the background that is completely opposite of the gate where the characters exit, there are two cars obviously made of cardboard. Many times they can be seen by looking over Maria's shoulder. (02:22:05 - 02:25:35)
Audio problem: During the opening overture, right when the orchestra starts "Maria", you can hear someone sneeze in the background. It's easier to hear on the soundtrack but you still can hear it in the movie.
Continuity mistake: Near the end of the movie, when Maria (Natalie Wood) is kneeling over Tony's (Richard Beymer) dead body, watch the cross around her neck. first it's sort of tucked into the top of her dress, then it is on the outside. it goes back and forth several times.
Continuity mistake: When Bernardo is piercing Baby John's ear, it's obviously just him and the Sharks, but then in the shot from above, you can see all the Jets running to the rescue. Also, Ice is already there, throwing a Shark off Baby John.
Continuity mistake: In the prologue, when the Jets are talking about Tony, Ice goes, "Man, remember them fists the day we clobbered the Emeralds." you can see A-Rab with his arms crossed. In the next shot they're uncrossed and he crosses them.
Continuity mistake: During the scene when the Jets and the Sharks are chasing each other around, when the jets are in shark territory, 4 boys get splashed with yellow paint. When all the boys are back on the playground nobody is covered in yellow paint.
Continuity mistake: In the scene right before "cool" when the two girls are crying, when they enter the garage their clothes are different.
Continuity mistake: The blonde guys snapping fingers, one with a violet t-shirt and the other with a red shirt, stand close to each other, but half a second later stand further apart.
Answer: People would not come to the theater to see Marnie Nixon despite the fact that she has sung the lead roles in West Side Story, The King and I, and My Fair Lady. They'd rather see that darling girl from "Miracle on 34th Street" again (or Deborah Kerr or Audrey Hepburn) than an unknown with actual talent.
Myridon