Here's the illustrious Potions Master himself.  This is the drawing I finally got right.  If you're really interested in seeing all the drawings I got wrong that led up to getting this one right, I'll send them to you, but they're not going up here.

Here's Snape delivering his handiwork to one of the people he despises, in the presence of another person he despises.  What a fun job.  He looks like he's thoroughly enjoying it, too.

Looks like someone wants a word with Dumbledore alone, out of earshot of that annoying Head Boy.