Pensieves and other magic (wasRe: HBP (Snape's) old school textbook:

[potioncat]

No: HPFGUIDX 137041

 
> Alla:
> 
> Oh, but Potioncat, don't you remember that person can modify his 
>own memory before putting it in the pensieve? :-)

Potioncat:
Well, we've seen the memory can be modified before being bottled. We 
weren't shown how. In fact...I just don't remember (my poor memory is 
constantly being modified and I don't like it one bit!) do we even 
see how the memory is put into the bottle?

But if the memory was taken out of the head, and placed in the 
Pensieve, the memory in the head would already be modified. That 
wasn't the situation in Slughorn's case.

I realise this is one of our many "agree to disagree" points. But I 
think the "Worst Memory" is accurate, but incomplete. What I always 
wondered about is this:

Snape cuts James across the face and blood spatters, but nothing else 
is said about it! We don't see James wiping blood away, or curing the 
cut or crying out in surprise or pain.

 Hmmm, I wonder if it leaves a lightening shaped scar? Sorry, this is 
hardly the place to levitate, erm I mean hardly the place for levity.

Alla: 
> Oh, did I tell you that now I am almost convinced that Snape indeed 
> left Pensieve on the table for Harry to see?

Potioncat:
But to what point? And how was he to know they would be interrupted?

 
> > Tammy now:
> > There was a spell from Snape's potion book that was used during 
the
> > "Worst Memory" scene, but it wasn't Sectumsempra, it was 
Levicorpus.
> > So to me, it's clear that Snape had at least been using that book 
> for
> > a little while before 6th year. 
> 
> <SNIP>
> Alla:
> 
> Yes, me too. Especially because Remus says that many people in the 
ir 
> fifth year were using it ( paraphrasing loosely)

Potioncat:
And this seemed oddly casual, given that Harry had told Lupin about 
the "Worst Memory". I get the feeling Lupin knows something about the 
spells or about the Half-Blood Prince that he isn't telling. 

Here's one possible chain of events for Levicorpus: Snape invents it, 
teaches his Slytherin Gang, Regulus learns it and teaches Sirius who 
teaches James who uses it on Severus. But still, if Lupin is being 
truthful, lots of students learned it.