Snape's "sudden movement"

[alisonb2210]

No: HPFGUIDX 40366

I have a theory regarding Professor Snape's 'sudden movement' in GoF. 
(British paperback edition, chapter 36, page 613 The Parting of the 
Ways)

When Harry starts shouting the names of the Death Eaters he saw in 
the graveyard, Snape makes a 'sudden movement' but recovers himself 
quickly when Harry looks at him. 

Although i would like to think Snape is now on the good side, i think 
this may be a clue that he is not. We are supposed to think that 
Snape is the Death Eater that has "left the fold forever" (Voldemort)
but what if he isn't? Voldemort never referred to this Death Eater by 
name. In the graveyard scene he passes a few of the Death Eaters 
without comment and stops to talk to others. Snape could have been 
one that he passed without comment. 

The reason Moody/Crouch hated Snape? He told Harry when he arrived 
back at Hogwarts that he hates nothing more than a Death Eater who 
walked free.

Why does Dumbledore trust him? Dumbledore is good, but he's not that 
good. He's been mistaken before this.

And who may the Death Eater that left the fold be? i think it could 
be Fudge. When Snape shows him the Dark Mark on his arm this could 
have been a veiled threat to him. 

i'm probably wrong, but i think this is the sort of plot twist JKR is 
becoming well known for. I think this part of the book is somehow 
important and will come up again in later books. Are there any other 
theories regarding this? 

Alison. (newbie) :)