He watched with curiosity as Snape carefully tipped the bottle to one side, so that the minute amount of liquid in it gathered at the edge of the vial into a pool that was  justdeep enough to cover the tip of the pipette. When Snape removed the bottles stopper, Harry found that the liquid that had been inside was barely enough to fill half of the pipette’s tube. Snape’s brow was furrowed in concentration as he carefully hovered above Harry’s neck.