Continuity mistake: When Elvis is at the pool singing "you're so square baby I don't care" watch his guitar player Scotty Moore sitting behind him. They use two camera shots for the scene. In one shot he has sunglasses on, in the other shot they are gone. This happens throughout the entire song.
Visible crew/equipment: During the "How Long Has This Been Going On" number, Hepburn dances by a mirror - reflected in it are the camera crew, desperately trying to get out of the image.
Continuity mistake: When Fred Astaire and Cyd Charisse are dancing among the parallel bars, her skirt changes to cullottes then back again to an ordinary skirt.
Continuity mistake: The character Sid Sorokin sings the song "Hey There" into a dictograph machine. He then plays it back and sings a "duet" with himself. However, the lyrics and melody at the end of the song are different from what he sang into the machine originally.
Continuity mistake: When we first see the "No Wolves Allowed" sign at the House of Bricks, "No Wolves" is on top and "Allowed" is at the bottom. When The Big Bad Wolf is looking at the sign, the words "No Wolves Allowed" are now on top of each other.