In the number "With a Little Bit of Luck", as Alfred Doolittle walks to the left side of the screen and sings, "They're always throwing goodness at you, but with a little bit o' luck a man can duck," the camera pans far enough to the left to reveal the tracks of a modern rubber tire in the dirt, probably made by the camera dolly or a mobile light stand.
As Eliza collects coins from the ground just before the "Wouldn't It Be Loverly" number, a man in the background standing on a cart calls out, "You're no Eastender, kid! We've got a bloomin' heiress in our midst." There's an odd extra syllable between the two lines, which explained by the subtitles (on the 1998 DVD release); these read, "Shouldn't we stand up, gentlemen? We've got a bloomin' heiress in our midst." Presumably the subtitles are based on the original script and/or dialogue track, and the first sentence was spliced out for the final release, in favor of the "You're no Eastender, kid!" line.
When Eliza is singing the last reprise of the chorus of "I Could Have Danced All Night" in bed, her lips often are moving slower than the words are being said and she is seen dragging a little bit when some of the longer notes are being held.
When Eliza sings "I Could Have Danced All Night", she goes into the bathroom, turns on the tap, and wets a washcloth which she presses against her chin and neck. She never turns off the tap, and it is still running as she exits the bathroom. In the next shot, you see one of the maids turn off the bathroom light, but she doesn't lean over and turn off the tap.
In the early scene where Eliza offers to pay for lessons, Higgins tells her, "Sit down!" and points across the room to a chair. He points with his right arm. In the next shot, Higgins is pointing with his left arm.
When Eliza exits Mrs. Higgins' garden after singing "Without You", she goes through the gates that lead inside the adjoining room. They are left swinging behind her. When the camera turns to Higgins immediately after, the gates are perfectly stationary. There was not enough time for the gates to stop swinging in the small amount of time between the two shots.
When Eliza is singing "I Could Have Danced All Night," the maids are furiously trying to dress her into the nightgown. Her right sleeve is tied but the left remains untied until she exits the bathroom where it's tied.
When Higgins comes home after the Grand Ball, he takes off his shoes as clearly seen in a shot in which he is sitting and lifts both feet off the floor. Later near the end of the song, he performs a similar move and his shoes are back on.
During "The Rain in Spain", you can hear Audrey Hepburn's voice mixed with Marni Nixon's voice. It's especially obvious the first time she properly sings, "The rain in Spain stays mainly in the plain," after Higgins' line, "I think she's got it, I think she's got it."
The goof item below may give away important plot points.
Crew or equipment visible
In the final scene Prof. Higgins is alone in the room, sitting in his chair, a shadow that appears to be Eliza's is visible on the floor as she approaches. It is mentioned by Gene Allen on the DVD that the shadow is actually his.