He sees alice or bob with two butter roses on top of a smaller piece. Charlie has the first cut, so he can cut horizontally and make a tiny piece with 3 butter

He sees alice or bob with two butter roses on top of a smaller piece. Charlie has the first cut, so he can cut horizontally and make a tiny piece with 3 butter roses on top. he either gets his three butter roses or a bigger piece of cake, their relative value is still the same for him.