“Snape had seen me crossing the grounds with Madam Pompfrey one evening as she led me toward the Whomping Willow to transform. Sirius thought it would be, uh, amusing, to tell Snape all he had to do was prod the knot on the tree trunk with a long stick and he’d be able to get in after me.” -Remus Lupin, Chapter 18, The Prisoner of Azkaban
This quote is generally interpreted as all happening at the same time, and that’s, I think, where it stops making sense, and why I have such difficulty incorporating it into Sirius’ character. That Sirius would do something thoughtless, reckless, and boarding on cruel–especially at this age–makes sense (and I’ve written about his mindset on this here), but actively sending a known enemy in after one of his best friends, to follow him when he’s most dangerous and vulnerable, potentially making said friend a murderer? That doesn’t make sense. That isn’t a prank. What possible “amusement” could have come out of that? Sirius very, very adamantly expresses in all other moments that he’s present in the books an unflinching loyalty to his best friends, and the prank hurts Remus as much as Snape. This doesn’t add up.
Further, and also important: why would they have this conversation in the first place? They’re enemies with no known trust between them: why would Severus trust that Sirius was telling the truth? This interpretation of the prank not only makes Sirius unreasonably cruel but it makes Snape gullible and stupid in a way that doesn’t line up with his character either.
With a slight adjustment to how this is interpreted, I think the prank remains cruel and stupid and everything that could cause Snape to interpret it as a murder attempt and hate them for it, one that would require James to come save him, but that also make Sirius’ intentions line up with the bullying pranks of a dumb fifteen-year-old and not straight up murder. Sirius was a bully as a teenager, no doubt about it, but he wasn’t evil.
So from here I’ll be playing the prank as:
- Sirius said to go in after Remus, but seeing as Snape had already seen Madam Pomfrey and Remus going to the tree, the full moon had already passed. “Going in after Remus” doesn’t necessarily mean “follow them in immediately on a full moon.” It could also mean literally: go in any time after they did. See what’s in there. Wouldn’t it be better after all to go sneaking around and find out what they’re up to when there aren’t adults (Pompfrey) around? (or bullying kids who could get in the way of your investigation) So it would have to be another time.
- Sirius, assuming he had 30 days (or however long was left after Snape confesses what he saw) until it was a problem again, and that Severus already knew that’s where Remus went and likely would follow them when it was most dangerous if not intercepted, comes up with a plan.
- Likely, Severus said something like “I know you’re all sneaking around and I’m going to figure out why” etc. etc. and Sirius snapped back “You know what, fine: come find out. I dare you. Go to the tree if you’ve got the guts…we’re going tonight if you’re not too much of a coward.” And he tells him how to do it. It is not a full moon when he says this.
- The plan was to act like a “ghost” once Snape reached the Shrieking Shack. As it’s supposed to be the “most severally haunted building in Great Britain,” Sirius thought it would be funny (and get Snape off their backs) if he leaned into this and attempted to scare the shit out of Snape on the other side. He’d have loved nothing more than to make Snape leave terrified and would think that would keep him from coming back (and be amusing to Sirius in the meantime)
- Well Snape isn’t stupid. Why would he show up when a known enemy tells him too? He doesn’t come that night. Or the next. He uses what Sirius told him, and like the clever Slytherin he is, he waits for the right time: he follows Remus and Madam Pompfrey next time the full moon is about to rise. Sirius, in the mean time, assumes that when Severus never showed, he simply chickened out.
- Sirius, as he and James and Peter prepare to meet up with Remus later that night, tells the story, not realizing the consequences at all. “At least Snivelus won’t be sneaking around following us tonight. Little coward didn’t even show up when I told him how to get past the Willow,” he says to James. And James realizes what a stupid thing his friend had done, realizes that Sirius might have meant for it to happen on a specific night–not tonight–but he’d still given him all the tools he needed to follow Remus, to find out the truth. James goes after Snape and saves him.