Opening the door, he was greeted by an array of no less than a baker's dozen of potions, and poultices, and balms, and oils - all of them lined up side-by-side on Snape’s desk, with a roll of parchment placed neatly in front of them. Harry’s gaze was drawn immediately to the first item in the row: while all of the others had a number written neatly on their fronts (from one to twelve), and were of a decent size, this one had no number, and was tiny in comparison. Approaching the table, and the Professor stood in front of it, Harry could see that the incredibly small bottle, which was stoppered with a pipette, had only a dribble of fluid in the bottom.  What was that?