From Aesop's Fables.

The Birds, the Beasts and the Bat

The birds and the beasts were at war. Their battles were fierce and frequent. Sometimes the birds won, swooping down out of the sun and attacking the animals. Sometimes the beasts won, creeping up on the birds as they searched for good on the ground, and leaping on them.
But there was one creature who was always on the winning side. He never lost, because he kept on changing sides. He would fight for the birds until they looked like losing, and then change sides. For a time he would fight for the animals, and then if the birds gained the upper hand, he would change back and join them.
This creature was the bat. He thought he was a very clever fellow, always being on the winning side.
In the end the war ended. The birds and the beasts agreed to live in peace for ever.
"Now I shall get my reward," the bat told himself. "Everyone will think I'm a fine fellow. After all, I was never on the losing side. I helped both sides. In fact, the birds and the beasts may make me their king!"
It did not work out like that at all. Neither the birds nor the beasts would have anything to do with him!
"You are a traitor!" they told the amazed bat. "You are loyal to no one. You only serve yourself. You let down both sides in the war. We want nothing more to do with you."
From that do to this the bat was an outcast, ignored by both the birds and the beasts.

Moral: People are expected to be loyal and to stick by their friends.

I was amazed at how much this was like Snape in Harry Potter. Even the bat-imagery. This is why I don't think that Snape only working for himself will work in the series. This is also the reason I believe that Snape is true to Dumbledore. If Snape were evil, then all of J.K's comments about not judging a book by its cover (pardon the pun) will have been in vain, and if Snape doesn't actually CHOOSE a side (because its our choices that matter), he won't be considered 'good'.

Anyway... ya.

Peace,
Rotae