Just finished re-reading HBP now, and was thinking after I read the scene between Maljoy and Dumbledore...
Malfoy tells DD that Snape made the Unbreakable Vow to his mum.. yet Dumbledore counters with saying that Snape is only working for DD and kind of disregards what Draco said.. so does thist mean that DD didn't know that, or he just didn't want to say it in front of Draco? Because of course, Dumbledore knows what happens if you break an UNbreakable Vow, so.. was just wondering...if he had known that.. maybe that's why Snape did the curse on him? Just a thought, i had thought this before but decided to share it here...😛