When Elmer pulls a carrot out of his pocket, it has a single stem with no leafy material. He then lays it down by Bug's hole and creeps away to hide behind a tree. But when Bugs sticks his hand out to get the carrot, it has several stems and a lot of leafy material.
At the end of the cartoon, Bugs Bunny is chewing on a very short carrot. When he starts to use his carrot as a flute and march away from the audience the carrot is suddenly much larger.