Burns watches Joey "escorting" Homer out of the plant after Burns reads the insulting letter. Speaking to himself, Burns says "I could crush him like an ant"
As he says this, from the camera's point of view, (probably Burn's also) Burns "crushes" Homer with his hand, who appears about the size of an ant from the upper level office.
Awesome writing like this makes the Simpsons great and Burns an awesome character.