Random Thought About Snape.I know this may sound incredibly stupid but it just occurred to me.More Like This
The reason that Dumbledore never allowed Snape to be Defence Against the Dark Arts teacher was because the position was cursed so that no teacher could last more than a year, and Dumbledore wanted to keep Snape around, wasn't it..?
As I said, I may sound a bit dense by only just realising this, but still... I love little intricate details like that. The whole plot has sense and reason behind it.
Then again I could just be making this up