The Train Scene GoF/ Sirius, Snape and werewolf incident/ Quote from PoA.

[zgirnius]

No: HPFGUIDX 162512

> Alla:
> Come to think of it Why would the "James not saving Snape life" not 
> be true, if Snape may have no chance to use it?

zgirnius:
I fail to see how he could not have a chance to use it, unless James 
somehow prevented it. Which would certainly change the tenor of the 
story. You're supposing he knew what he would be facing.

Alla:
> "They planted the Whomping Willow the same year I arrived to 
> Hogwarts. People used to play a game  trying to touch the trunks. 
In 
> the end, a boy called Davey Gudgeon nearly lost an eye, and we were 
> forbidden to go near it. No broomstick would have a chance" - 
p.186, 
> PoA, paperback, am.ed.
> 
> Again, I don't have any thoughts about it, I just find it strange 
and 
> I don't know why.

zgirnius:
The line does not seem strange to me. I see it as playing a couple of 
different purposes. In the context of PoA, it establishes the Willow 
as a danger (which Our Heroes will later face) and is a clue for 
those subtle enough to look for 'em (not me, I rip through the books 
to see what happens next!) that the Willow is somehow connected with 
Lupin. The second purpose is relevant to our discussion. It indicates 
that Snape was knowingly breaking a school rule when he went into the 
passage, above and beyond merely being out past curfew.

Of course, in my view it was a rule he had reason to believe the 
Marauders broke regularly, so he thought he had the knowledge (once 
Sirius told him how to deactivate the tree) to handle the dangers 
safely.