Snape's predicament: The DADA jinx and the Unbreakable Vow

[pippin_999]

No: HPFGUIDX 136553

Carol:
And we know that it was Kreacher who told Voldemort of the bond 
between Harry and his godfather.

Pippin:
One very important fact needs to be added to this excellent analysis.
Kreacher did not report directly to Voldemort. His conduit was
Narcissa.


So...
if Snape is lying about being the source of the information about 
Sirius, and he obviously is, it can only be with Narcissa's collusion.
Snape must be also be sure that Bella has not been told about
Kreacher. That can only be the case if *no one* in Voldemort's
camp knows about Kreacher, except Narcissa herself. I can
see her whispering the information to Lucius as some bit of 
gossip she picked up somewhere.

This means that the encounter at Spinner's End cannot have been Snape 
and Narcissa's first discussion of Draco's plight. Narcissa's
performance reeks of bad acting (though some fans have been 
more inclined to blame bad writing.) But Jo has played that trick on
us before, at the end of CoS, where Ginny dissolved in a flood of 
OOC tears and claimed to have had no knowledge that the Diary was 
dangerous. A lie, of course, since she tried to destroy it and then 
stole it back from Harry.

That opens the possibility that the Unbreakable Vow was planned in
advance  as well. What if it was  suggested originally not by Snape
or by Narcissa but by Dumbledore himself, as a way to ensure that 
Snape would be able to keep watch over Draco without  Voldemort 
calling him off?

 But Dumbledore, being far cleverer than the ordinary man, makes
mistakes that are correspondingly huger. He did not foresee that 
Narcissa, in her great fear for Draco, would compel Snape to vow 
to carry out the task if Draco failed.

I don't think either Snape or Narcissa knew exactly what Draco had 
been told to do. I think Draco had been bragging, the way he was with
Pansy, and sneaking off to secret meetings with Bella as he was with
Borgin, in a way that troubled Narcissa enough to take her suspicions
to Snape. If Narcissa had known for sure what Draco was supposed to 
do, she wouldn't have been afraid that it was a trap, she would have
been sure of it. 

However I think both  she and Snape suspected that Dumbledore was the 
target, and that became certain after Draco's train-stomp. If Draco
had wanted to kill Harry, he could have. 

It is after all this that Dumbledore starts teaching Harry about the
horcruxes. I think Dumbledore thought he and Snape could outwit the 
vow, but even if they did, it would have to *look* as though
Dumbledore had died at Snape's hands, or Voldemort would kill Snape 
for his disloyalty. Whatever happened,Harry would have to continue
the hunt on his own.

I don't think Dumbledore planned to die that night. But Snape would
know, being the potions master, the signs that someone was in
extremis from poisoning. At the time when Snape arrived on the tower, 
he was out of choices. If he tried to save Dumbledore, the vow would
kill him, Dumbledore would still die, and Harry would be left
paralyzed and helpless on top of the tower with four DE's, none of
whom were so keen on following Voldemort's orders that they could 
be trusted to leave Harry alone. And yes, I think Snape knew that
Harry was there. He could certainly see the other broom as  well as 
Draco did. 

Pippin