Ella's red shoes change from 2 inch heels (in the Cha Cha Cha and Just in Time numbers) to 3 inch heels for the non-dancing sequences in between and afterwards.
After she talks on the phone to Jeffrey Moss, Ella stands up from the switchboard and walks around the room singing. When she returns the switchboard has changed place.
When Jeffrey cleans a spot on the mirror, his left hand is leaning on the wall next the mirror. In the following shot his left arm is by his side.
When Ella leaves with her suitcases, her hair is mussed from performing her song, but when she returns it is neatly in place again.
At 2:34, the telephone is shown with the cord wrapped around the phone so that the bottom of the handset is on the right. At 2:39, when the woman taking a shower rushes over to answer the phone, you can see that the handset has switched position so that the bottom is now on the left.
As Jeffrey Moss changes the paper as he works on the outline for "The Midas Touch," the carbon paper between the blank sheets is shiny-side up. This would give him a mirror image on the back side of the first sheet instead of an original and a copy, which as an experienced typist, he would surely know.
While Jeff is singing "I Met a Girl," various people in the background can be see mouthing the words along with him.
When Ella first visits Jeff's apartment, she produces a cup of coffee from her purse despite that she dropped the purse to the floor after first seeing him. Also, the purse gets caught on Jeff's feet when he rolls over to go back to sleep and falls to the floor a second time.
When Ella rips off all the frills on her La Traviata red dress, there are no rips in the fabric or threads showing.
During the "gathering of the bookies" scene in a basement, Eddie Foy Jr.'s speech is backed up with the hissing of steam and the clinking of pipes. As soon as the pre-recording of "A Simple Little System" begins, all vestiges of the hissing of steam and the clinking of pipes miraculously cease until the final fade-out.
When Jeff (Dean Martin) is singing "I Met a Girl" while crossing the street in front of taxis, the words he lip-syncs don't match the music's soundtrack.
After Ella jumps on Jeffrey on the couch and begins kissing him, a moving shadow of the camera falls across them as it moves to the right.
When Jeff contacts Susanswerphone from Brooklyn Heights, he speaks with Sue, "the other one", but Sue is supposedly out with Otto at the Crying Gypsy Cafe, not working the switchboard.
Ella tells Jeff that she used to procrastinate by sharpening her Ticonderoga pencil down to the T (or rather the "tuh"). However, Dixon Ticonderoga say that their pencils have always read from point to eraser, so the T would be the *first* letter to disappear.
In the song "Simple Little System" a background extra dressed as a maid is reading all the song lyrics from her book. This same extra (who is in the center of the frame all the way in the back at the very end of song forgets to drop her book on the word "System" with everyone else then drops it several beats later then doesn't shake her hands on the last note and doesn't freeze in final pose to wait for "cut" and drops her hands then tries to sneak them back up in the air.
At c.98 minutes Ella (Melisande) leaves the party by the back gate. This was locked when she and Jeffrey Moss arrived earlier that evening.