In the scene where the tin man is dancing, and the camera zooms back to Dorothy and the Scarecrow several times, at one point there is a fuzzy yellow thing in the corner (probably a microphone) that is leaning in on the scene.

The camera will zoom back to the tin man. When it comes back to Dorothy and the Scarecrow, you can see a man walk on in the corner for one second, then off again. Whoops!