I was thinking about Snape's mission for the order.Maybe he disguises himself as a deatheater cause they always where masks.Snape already has the dark mark. Also voldy can't read his mind because he knows occlumcy.He knows everything about the deatheaters.All thier rituals and dislikes it would be easy for him to trade places with an already captured deatheater and just to be sure he could use a polyjuice potion.He is a potions master.

Though the Polyjuice Potion tricked Malfoy, I doubt Voldemort wouldn't see past it. He knew each of the Death Eaters that arrived, even though their faces were covered (or maybe he knew because of their position in-line, seeing as he recognised the unfilled spaces). It'd have to be something pretty amazing to trick Voldemort, I reckon...

I was under the impression that Snape was "Malfoy's" pawn. Kissing Malfoy's butt. I believe that Malfoy is covering for Snape, saying that snape is on the inside of Hogwarts, and was trying to persuade Dumbledore to trust him. Malfoy would be the go between between Snape, and Voldemort. Also we know Snape is a trained Oclumen. He can lie at will, and the Dark lord can not pierce into his mind. Then again, he could be lying to Dumbledore to.

"Make way for the Heir of Slytherin, seriously evil wizard coming through. . ."-Fred and George(CoS)

I see Snape more as playing Dumbledore than Voldemort. I do agree with Vernon that I doubt polyjuice would fool Voldemort. Even as an Occulumens, I don't think Snape could completely trick one of the world's most powerful wizards with a simple potion. Locke is also right in that at least in the books, they give the strong indication that Snape is having the Order believe he's spying through Malfoy. However, now that Malfoy has been arrested, I wonder how he's going to keep up the impression that he's spying on Voldemort. I personally believe he's still working for Voldemort and against Dumbledore, so I think it will be interesting how he sells his story to Dumbledore with Malfoy gone.

Hehe, Helen, 2nd post in which you have said vernon instead of venom I was also wondering how snape would manage. I can't totally decide which side snapes on. It all depends on "why" he switched sides in the first place. The general concensus is because, Voldie was going after Lily, and snape informed dumbledore because of it and switched sides...(that whole persues evans thingy) but i don't know anymore.

"Make way for the Heir of Slytherin, seriously evil wizard coming through. . ."-Fred and George(CoS)

I have a hard time believing that Snape (as good an Occlumens as he is) could be blatantly hiding the fact that he is, in fact, on Voldemort's side. Dumbledore himself has said that he know Occlumency, and he does always seem very proficient in most 'magical areas'.

I don't have any ideas as to why Snape decided to switch sides. The Lily Evans theory seems very fan fiction to me, but it does appear to be the most fitted idea, compared to others I've read. What I have been wondering lately, though, is why Snape decided to become a Death Eater at all. He doesn't strike me as the sort of person who'd walk up to Voldemort and say, "sign me up, mate, I want to be a Bad Boy Death Eater...and maybe if I kill a few people I'll get given a 'special power' I don't already have, from a man who could take it away as quickly as it was given."

But with an author like J.K., one can only guess.

Who knows what JKR will reveal about Snape.  I still kind of like the Snape as Voldemorts son idea.  It might account for Voldemort cutting him some slack in terms of his 'lack of loyalty' (assuming Snape is good or neutral).  I think we are meant to feel that both Voldy and D could detect a lie or the truth from Snape.  It would seem that in order for Snape to disguise his true afilliations, he would need to avoid both of them as much as possible and get or give his information to intermediaries, such as Malfoy or Lupin.  If he can keep away from the guy(s) he is actually trying to fool maybe that extends his life(if he's working for the Order) or his value (if he's working for the DE's).