Snape, Quirrell and Voldemort

[acciosirius]

No: HPFGUIDX 73665

OK - I'll start off with apologizing if this has been discussed 
before...

I've been very curious, after going back and re-reading all five 
books, how Snape would be able to go back and successfully 
reintegrate himself with Voldemort and the Death Eaters? In SS/PS, 
he is found to be threatening Quirrell and asking him where his 
loyalties lie. Now, how, after making it pretty obvious that he's 
against Quirrell getting the Stone for Voldemort, is he able to go 
back to the fold and spy again, when Voldemort would know that he 
was working against him in SS/PS? 

I'm very interested to hear what you all think! Thanks! 

Jen (Who would be interested in hearing Snape say, "Well, you know, 
my Lord, I really only thought he wanted it to make the gold...") :-)