Remus Lupin: Has it occurred to you Harry, that Snape was simply pretending to offer Draco help so he could find out what he was up to?
Harry Potter: That's not what it sounded like.
Nymphadora Tonks: Perhaps Harry's right, Remus. I mean, to make an Unbreakable Vow...
Remus Lupin: It comes down to whether or not you trust Dumbledore. Dumbledore trusts Snape, therefore I do.