Understanding Snape

[houyhnhnm102]

No: HPFGUIDX 153901

Lunasa:

> Right... Okay... I could be wrong, but for some 
> reason I've always read that scene as Lupin's sitting 
> at his desk waiting for Snape to come with the potion, 
> he takes out the map and gets a huge shock by seeing 
> that Harry, Ron and Hermione are in the Shack with 
> Black and... Dun dun! Dead of 13 years Peter Pettigrew! 
> Lupin then gets up and heads off to the Shack. Snape 
> then comes to Lupin's office, sets the Potion down 
> plans on waiting for Lupin to make sure he drinks it, 
> spots the map, looks at it, sees Potter and his gang 
> in the Shack with Black and a dead man! And then he 
> spots Lupin on his way to the Shack, probably looks 
> out the window and sees Lupin on his way there! [snip]

> But anyway, Snape would still have seen Pettigrew's 
> name on the map What exactly would he thought of that? 

houyhnhnm:

Lupin says, "I was watching it carefully this evening 
because I had an idea that you, Ron, and Hermione might 
try and sneak out of the castle to visit Hagrid before 
his hippogriff was executed."

"I watched you cross the grounds and enter Hagrid's hut. 
Twnety minutes later you left Hagrid, and set off back 
toward the castle.  But you were now accompanied by 
somebody else...and then I saw another dot, moving fast 
toward you, labeled /sirius Black/ ... I saw him collide 
with you; I watched as he pulled two of you into the 
Whomping Willow--"

Later Snape says, "I saw you [Lupin] running along this 
passageway and out of sight."

So Pettigrew was already in the tunnel when Lupin was 
still sitting at his desk.  Lupin was out of the castle 
and in the tunnel by the time Snape saw the map.  There 
is no way Snape could have seen Pettigrew.  It also 
sounds as if Lupin had spent a considerable amount 
of time watching the map, more than the 30 minutes 
or so accounted for by his statements.  The Trio would 
have to have made their visit *before* the scheduled 
execution and Lupin wouldn't have had any way of knowing 
how long before.

But, as always when I look back through the books to 
answer one question, I come across a passage that raises 
another.

Lupin says, "As long as I take it in the week *preceeding* 
the full moon." [emphasis added] So why did he need the 
potion on the night of the full moon?  Had he been taking 
it during the preceeding week?  Does he have to take it 
every night from the week preceeding the full moon until 
the moon wanes?  If you miss a single dose, does it fail 
to work at all?