When Millie and Jimmy take the car on a wild joyride after the dance, they pass the same cars and same pedestrians passing the same locations multiple times.
Miss Dorothy arrives at the Priscilla Hotel on a Thursday (from the calendar). That night, she goes to a friendship dance with Millie. The notice in the elevator advertises dances on Saturdays.
When Muzzy is flying through the air after being shot from a cannon. She has on a silver colored suit and helmet. After she lands on the stage the suit and helmet are both gold colored.
When Mrs. Meers is first spraying chloroform in the room without the gas mask, she faints and falls over backwards. When Miss Dorothy comes into the room, she is snuggled up on the bed holding a doll.
When Mrs. Meers passes out in Miss Dorothy's room, the light beside the bed is on. When Miss Dorothy finds Mrs. Meers passed out on her bed, the light is off.
A Jewish wedding would not take place on a Friday night.
The "Tapioca" sequence lasts almost 7 minutes but a 78 RPM record, which is providing the music, plays for a maximum of 3 minutes.
During "This is 1922," the calendar by the reception desk at the Priscilla Hotel says Thursday, 2nd June. In 1922, June 2nd was a Friday.
When Muzzy sings lower and lower notes it causes a martini glass to break suddenly. But glass is broken by its resonate frequency - the note it makes when it's rung by tapping it sharply. A much higher note than Muzzy's is needed to break a martini glass.
The film is set in 1922. The calendar in Mrs. Meer's registration desk says June 3, a Tuesday. In fact, June 3rd in 1922 was a Saturday.
When Jimmy and Millie are sitting on the ledge outside the office, the flagpole which both fell onto a few moments before is nowhere to be seen. That's because they have come off the flagpole onto a ledge well below it.
When Millie and Jimmy are sitting on the ledge of the building and he leans forward, you can see through the top of his head.
When Jimmy and Millie first start dancing the Tapioca, Jimmy kicks the phonograph to stop the record from skipping. At that point, the phonograph's needle is close to the center of the record meaning that there should only be a few seconds left of music before the record ends, yet this is the beginning of a song lasting several minutes.
At the end of the movie, when the man is falling from the chair, which is on Jimmy's shoulders, the ground is moving.
During Muzzy's acrobatics act, wires used to safely propel her through the air are seen in the close-ups.
Several times during the movie the bald caps worn by Jack Soo and Par Morita are clearly wrinkled, particularly at the back of Morita's neck.
Millie drives a red roadster (with a drugged Mr. Graydon beside her), chasing the the laundry truck. As Millie makes a right turn from a T-junction, a modern blue-grey station wagon can be seen parked on the top left side of the intersection.
Although the song tells us "this is 1922," all of Millie's
post-transformation fashions are from 1927. Her seamless stockings first appeared in the 1950s.
The baritone saxophone that Muzzy plays is a low A baritone saxophone. Such saxophones did not exist until the 1950s.
When Millie and Jimmy are hanging on the flag pole, the U.S. Trust Company at 45 Wall Street (built in 1958) is the first building on the left.
Jimmy Smith's boss' "red roadster" is a 1925 Pierce-Arrow Model 80. The Model 80 was manufactured by Pierce-Arrow for the 1925 through 1928 model years, when it was superseded by the Model 81. No Model 80 Pierce-Arrows had been manufactured in or before 1922, when this movie was set. Unlike most brands of automobiles at the time, the headlamps of Pierce-Arrows were installed in fender-mounted moldings.
When Millie and Miss Dorothy are walking toward the elevator just before the Jewish wedding scene, Millie says, "Have you forgotten about the wedding tonight? I'm singing," but her mouth doesn't move.
As Millie and Miss Dorothy get to their rooms for the first time you can see the shadow of the camera assembly on the left wall of the hallway as it pulls to a stop.
When Jimmy is hanging off the flagpole on the side of Millie's office building, the secretary out of the window tells him that Millie is located on the twentieth floor. Jimmy, seemingly not knowing this information as he counts the floors on the outside of the building, should already know it as he had been to see Millie in her office at least three times before.
When Millie and the others are being chased as they are trying to escape from the Chinese opium den by Mrs Meers and the Chinese laundry men, she says to her companions, "Heading for Long Island and their rich society friend". Never had their been any interaction or even mention to Mrs Meers of Muzzie.
It's never explained why Millie, supposedly an American girl, has a strong and obvious English accent.