Why did Snape take the UV?

[a_svirn]

No: HPFGUIDX 156865

> >a_svirn:
> But that's just it â€" the risk wasn't  manageable and if it was 
> calculated we are still in the complete dark about  the nature of 
> those calculations. If it were manageable risk he wouldn't  have 
> ended up stuck with the third provision. He did, after all,  
> neglected to negotiate the precise wording. Rather careless of 
him, 
> I'd  say. In fact, why did he have to agree to the third provision 
at 
> all? If he  didn't want to, he didn't have to, did he? <snip> 
> <snip> 
> As for Snape's calculations we have to assume that he 
miscalculated  
> rather badly. If, that is, we are dealing with the DDM Snape. 
> However,  I, for one, don't see how he can not be "remotely 
stupid" 
> if he didn't  anticipated the trap of the third provision. At the 
> very least he should  have been naïve in the extreme not to smell 
a 
> rat as soon as Narcissa  mentioned the UV. <snip>

> Nikkalmati: 
> This IMHO is confusing hindsight with the calculations made at the 
spur of  
> the moment -- which is all SS had.  Of course, it didn't turn out 
well, but  
> for that I blame Bella, who interfered with Draco and prevented SS 
from finding  
> out from him his task and how he was going to carry it out. If she 
taught  
> him Occulmancy, it can only be to keep out SS.  I also think SS  
underestimated 
> Naracissa or at least her deviousness.  If he did not know  
Draco's task, he 
> could not anticipate how important it would be for Narcissa to  
trap him into 
> doing it, if Draco failed. 

a_svirn:
But if he didn't know about the task then the whole point is moot. 
Carol argued that he did know in which case he couldn't help but 
anticipate the third provision, IMO. 

> Nikkalmati: 
 We don't know enough about the UV  to know if SS 
> had any choice but to swear to part 3 once he had begun.  

a_svirn:
Well, Arthur Weasly was able to stop Fred and Ron after they had 
already started the ritual. 

> Nikkalmati:
 However, even if he 
> could have backed out, unless he anticipated the nature of  the 
task, there was 
> no overwhelming reason to stop and lose all he could gain  from 
making the 
> vow.  

a_svirn:
Which means that risk wasn't at all calculated and manageable. I'd 
say that this is in itself an *overwhelming reason* NOT to make the 
vow. Just what did Snape gain by taking it? The disadvantages are 
glaringly obvious, but what are the advantages? 

> 
> >a_svirn:
> <snip>. I 
> don't believe, however, that Snape  knew about Draco's mission. It 
> looks to me as though he skilfully drilled  both sisters in order 
to 
> garner as much information as possible. 
> Nikkalmati: 
> Agreed. 

a_svirn:
I am pleased you say so! Unfortunately, it still doesn't explain the 
UV itself...