Just before the Wicked witch sends out her flying monkeys she metions something about a giant bug. The bug was part of teh original movie but when it was released they cut the bug part out, however, they forgot to cut the witch's line about it.
To quote the imdb.com site, trivia for Wizard of Oz:
The film originally contained an elaborate production number called "The Jitter Bug",
which cost $80,000 and took five weeks to shoot. In the scene, Dorothy, the
Scarecrow, the Cowardly lion, and the Tin Woodsman are on their way to the Witch's
castle when they are attacked by "jitter bugs" - furry pink and blue mosquito-like
"rascals" that give one "the jitters" as they buzz about in the air. When, after its first
preview, the movie was judged too long, MGM officials decided to sacrifice the "Jitter
Bug" scene. They reasoned that it added little to the plot and, because a dance by the
same name had just become popular, they feared it might date the picture. The Witch
still refers to the bug in the final film, just before telling the Monkeys to "Fly!" Only
home movies of the filming of "The Jitterbug" survive, though the song is on current
versions of both the soundtrack CD and the recent anniversary edition videotape. The
sequence was also incorporated into a recent stage version of the musical.
Recently my high school did a production of the Wizard of Oz and the "Jitterbug" was in it. I was curious about it. I kept thinking "I don't remember this in the movie." Thanks for clarifying. =)
I was under the impression that the "Jitterbug" footage no longer existed. In the 1999 edition of the film (VHS), the 'making of' thing after the film says that the only existing records of that scene are home videos from the producer.
Okay, first, it wasn't a "giant bug" at all...
WITCH: Take your army to the Haunted Forest, and bring me that girl and her dog!...They'll give you no trouble, I promise you that. I've sent a LITTLE INSECT on ahead to take the fight out of them.
As for the actual point of this slip-up, I believe there is actually a reference to the "little insect" the witch sent. As the scene begins, the Lion gets bitten on the nose by SOMETHING, and the dialog goes as follows:
LION: What's that? What's that? Take it away - take it away - Take it away!
TIN MAN: Hold still - hold still --
These words are the beginning of the Jitterbug scene, and they are still in the movie. After this (in the original scene, not the final cut), Dorothy jumps as a bug bites her leg, then the Tin Man and Scarecrow get bitten, and they start to sing the Jitterbug song. (I read that in a copy of the movie script - I don't want to post an outdated link, so Google for it).
Granted, not much attention is paid to the remaining exchange between the Lion and the Tin Man, and it's not entirely obvious that the Lion gets bitten at all, but he does.
The reason the Jitterbugs was removed is because the movie was too long. They needed to cut some scenes. Originally they were going to cut the Over the Rainbow scene but some producers and whatever decided to leave it in and cut Jitterbugs instead.