After Grover smacks Porky with the stick/log, Porky's rifle flies up and lands in the path or road to Porky's left. After Porky puts the earmuffs on Mandrake, the rifle is suddenly in the grass to Porky's right.
When Porky shows Mandrake the picture/drawing of a groundhog, the image of the groundhog shifts and jumps inside the frame of the paper it is on.