Now that Rob knows the vial will make Mary more manageable, Rob pours half the contents of the vial down Mary's throat. Rob steps back as Mary begins to shrink. Mary's entire body shrinks at the same time. Inches and height are quickly lost to her.
In a matter of minutes, Mary has been reduced to half her previous size. She is still pretty large, but closer to what Rob thought he could manage. Mary is still panting, her udder still swelling slowly. Her reduced size hadn't relieved any pressure.
Rob then...