A Whole New Horizon

[Alessandra]

In Harry Potter and the Half-Blood Prince we are introduced to a whole new branch of magic: Non-verbal spells. That explains a lot, and is probably the only alternative to the wand-less magic hypothesis. In fact, a wizard just need to be holding his wand to perform this kind of magic.
Once again Snape reveals a very good teacher, giving us very useful pieces of knowledge!

[yvonne]

I wonder, is this done in the other books before, without our knowledge?
And could it also have something to do with that horrible scene in Half-blood Prince?