In "The Kaplowey Scroll", after Papa leaves with the scroll, a Smurf turns his head, revealing that the animation cel of Brainy in the background is cut off at the waist, which was not meant to be seen by the viewer.
In "The Kaplowey Scroll", after Clumsy has shown Papa Smurf the scroll, Papa goes to his lab. As he leaves, one of the Smurfs turns and Brainy Smurf's lower body and legs are missing.