Minor details about Snape in HBP

[d.]

No: HPFGUIDX 135102

While most people focus on the "is Snape evil or not?" grand debate, there're some tiny
details about Snape in HBP that tend to be overlooked. I wonder if these can add onto any
of the 10,000 theories that only Snape can spawned.

1. Harry remarked that Snape disagree with him on the best method to fight dementor. I
wonder if this would come up in book 7? What is Snape unorthodox way other than Patronus?
Or is this going to be one of many Snape's creative alternative ways (like his Princely
notes) to compensate his inability to conjure a powerful patronus because he seems too
bitter to have true happy thought, nor having a positive, strong father figure?  

2. Harry specially noted that Snape used an unknown healing spell that sounded like a
song. It heals Malfoy's deep bloody cut fast and well. No one in the series so far seems
to use this before (or I don't remember ever reading about it). It was stressed how near
perfect it healed facial wound that Harry wonder about it again at the end at hospital
room when he saw Bill's mangled face. What could the song-like healing spell be and if it
will come up again in book 7?  

D.