Froli pointed out, as we were watching the movie Harry Potter and the Prisoner of Azkaban last night, that there is a scene in that movie that should have ended the entire debate about whether Severus Snape is good or evil. And he is right, it should have.
Just in case you haven’t seen the movie recently, let me remind you: It’s the one where Sirius Black escapes from Azkaban, comes to Hogwarts in search of Harry, and where we met the Dementors for the first time. It’s the one where Hermoine meddles with time and where a certain Buckbeak plays an important role in the plot. The scene in question takes place right after Professor Lupin and Sirius Black have revealed that the rat Scabbers is in fact Peter Pettigrew, the one who betrayed Harry’s parents to Voldemort, and are dragging the traitor back to Hogwarts and the Dementors.
Sirius is enjoying the fresh night air and has just invited Harry to come live with him instead of with the Dursleys, when Hermoine notices that there is a full moon that night. That is bad, given Professor Lupin’s… condition, and he immediately begins to transform into a very unpleasant creature. Sirius tries to slow the change, and just as it finally completes, Snape comes up from the tunnel, unaware that there is a werewolf nearby, and beings scolding Harry. The werewolf interrupts him by snarling something that sounds a lot like “oh, more food!”
Snape immediately realizes that he is face to face with a werewolf, a creature he is deathly afraid of, and that there is nowhere to run, and nowhere to hide. (In case you haven’t seen the movie or read the last book yet, I’m going to hide the next few sentences, so if you want to read, you will need to highlight them. Fair enough?)
Snape’s instinctive reaction is to shield the children. He steps in between Harry, Hermoine and Ron, all of whom he detests, and a hungry werewolf, in an effort to protect them.