When George, after singing "I'm Making Headway Now" in the stables, places his ukulele into a wheel barrow and walks away, it is a totally different instrument to the one he uses to sing the song.
Obvious use of a dummy when George gets thrown about by the acrobatic troupe.
At the end of the film when 'Maneater' catapults George onto the roof of the horse box, the wire harness attached to his back is visible.