Why did Snape take the UV?

[Kathy]

No: HPFGUIDX 156868

The reason Snape took the vow were two-fold.

1.  It's a plot ploy so we know what an UV is when we find out
    a crucial point:

    Why does Dumbledore trust Snape?  Because Snape took an
    UV to protect Harry with his life.  To see my whole theory
    go to schnoogle.  It's a one shot (about 20 pages)under 
    Lady Pensieve.  

2.  Because Snape used Legilimens to read Narcissa's mind.
    He already knew what the plan was, but he had another
    plan with Dumbledore.  By taking the UV he knew that he
    could protect both Dumbledore and Draco at the same time.

KathyO


--- In HPforGrownupsI don't think SS knew Draco's task in Spinners End 
and took the vow (to protect Draco) to find out what was going on. If 
Narcissa trusted him and told Draco to cooperate with him, he could 
find out the task and thwart it. It was too important to pass up the 
chance to gain this information. I am relying on his surprise at the 
visit, Bella's surprise that he knew the task (he didn't), Bella's 
surprise he would take the vow, and the significant (to me <g>) pause 
when he looked out the window at the empty street (trying to decide 
what he would say to Narcissa). We don't have any reason to believe 
that LV would share
his plan for Draco with SS. LV is secretive, Bella seems to think it is
treasonous to reveal the task, and SS is not shown as being in favor 
with LV; otherwise, why is PP living with SS and openly spying on him?
Nikkalmati