Petunia knows Snape! Snape and Petunia and Lily knew each other as adolescents or perhaps earlier!; or, My brain surprises even me sometimes.

Petunia knows Snape! Snape knew Lily's family! How has this escaped me for so long?

Okay, here's how it all went down.

Snape and Lily knew each other as children. Either they met before Hogwarts, or they met at Hogwarts and became friends, but anyway they hung out together as children, and Snape spent some time at the Evans house so he knew Petunia as well. It seems likely that Lily would have been nice to poor misfit Snape at Hogwarts, since Lupin says in the third movie that she was an extraordinarily kind person with a gift for seeing the good in people even and perhaps especially when they could not see it in themselves. I kind of see Snape as enjoying knowing more than Muggle-born Lily about the wizarding world, and imparting his knowledge to her. As they got older, I think he started feeling uncomfortable about being friends with her, and it's plain from his memory that by their fifth year he was acting like an ass to her. He was in with the sketchy Death Eater kids sometime in school, and so on that basis he quit being friends with Lily even though he was plainly in love with her.

I am basing all this on a rather awkward conversation between Aunt Petunia and Harry in the fifth book. Petunia says that dementors guard the wizard prison, Azkaban, and everyone turns to her in astonishment, and she says that she heard "that awful boy telling her about them, years ago". Harry says that if she means his mum and dad, why doesn't she just use their names? Petunia appears to ignore him and seems very flustered.

We're obviously meant to assume that Petunia does mean his mum and dad, and that she is flustered about having revealed that she possesses knowlege on a subject completely anathema to the life she has built for herself. But I was reading it today, and I think there's something else going on here. The more I think about it, the more totally convinced I am.

The question Harry asks seems a trifle strange given the context. He's used to the Dursleys' being snotty about his parents, and surely the more important issue here is that Aunt Petunia knows about dementors! The fact that he brings it up, and particularly the phrasing of it, seems designed to draw our attention to the fact that Petunia isn't using names, which gives rise to the question: Who else could she be talking about?

Very important here is the information we get from Sirius and Lupin later on in the fifth book that Lily didn't start going out with James until the seventh year, when he "deflated his head" a bit. Until then, she obviously thought he was a bit of an idiot (even if, as Rowling has suggested, she liked him more than she acted like she liked him in Snape's memory). The phrase "awful boy" is suggestive to me. Petunia has never used the word "boy" to describe James; she and Marge and Vernon have all only ever (as far as I can recall) referred to him as "Potter". "Awful boy" sounds diminutive, like she's talking about a kid, certainly younger than James would have been when she first met him (at least seventeen when he started dating Lily). But that in itself is something of a semantic quibble, and it's certainly not outside the realm of possibility that Petunia would call him that.

Here's what really gets me. She heard the awful boy "telling" Lily about the dementors. Not talking to her about them, telling her about them. If she was talking about James, then James and Lily would both have had to be seventeen years old and in their final year at Hogwarts. (Or older - we know they started dating at seventeen but we have no idea when Lily first brought James home to meet the folks.) It seems incredibly unlikely to me that any witch attending Hogwarts, let alone a very clever and talented one like Lily, should make it to year 7 without knowing about dementors. In the third book when dementors first show up, many of the students seem unsurprised by them (Ron and his brothers plainly already knew about them), and I'm guessing that Hermione, for one, already knew they existed. Surely Lily would have known about dementors by the time she started dating James.

What seems much more likely, given that Lily is from a Muggle background, is that Snape was telling her about them when they were much younger, in their early years at Hogwarts. Snape was "the awful boy", and it really was years ago, dogs' ages, even before Lily met James, back when Lily and Petunia were in their early teens. Snape spent time at the Evans home, and he told her things about the wizarding world with which she, as a Muggle-born, would have been unfamiliar, like dementors.

This seems tremendously significant but I don't know why. I bet Petunia knew that Snape had a crush on Lily. I just wonder why this is all important. Something to do with Dumbledore's having occasion to correspond with her before the Potters died. Something to do with Snape's having been in love with Lily.

Good theory, eh? Aren't I clever? Interpreting these little peculiarities of conversation with a keen eye? You thought you could fool me, JK Rowling, but I SEE RIGHT THROUGH YOU. (Sometimes.)

Also, I love Lupin. I hope he survives.