How and when did Snape learn Occlumency ?

[potioncat]

No: HPFGUIDX 116461


>>>Del wrote:
 So could it be that Snape taught Harry in that weird way (making 
him more angry at the start of the lesson) because it was the way he 
learned Occlumency himself ?
 
 Anybody have any answers or additional questions ?
  Del, who thinks of what it would mean if Snape had already been a
 Legilimens at the time of the Pantsing and/or the Prank...

Potioncat:
These are good questions.  I wonder if it's something JKR will tell 
us?  If Snape already knew curses that 7th years didn't know when he 
came to Hogwarts, he may have had time and interest in learning 
something else obscure.  And it could have been his Head of House 
who taught him. One of his parents could have taught him. Or he may 
have learned it as an adult from some other mentor....even in the 
past 14 years at Hogwarts. Or is it possible that having the 
potential skill for it, he developed it as he matured? What if he 
accidentally learned to shut off certain thoughts under certain 
circumstances?  (Being bullied by his father?) Sort of the way Harry 
grew his hair back?

I don't think we know he is an Legilimens, although there are hints 
that he might be.  He uses that spell, with a wand while teaching 
Harry.  But LV doesn't need a wand to do it. 

I think he knows Harry is not telling the truth during the scene 
with the petrified cat.  Although I don't think he could get all the 
details.  Same for the scene in GoF where he makes Harry sit near  
his desk and threatens him with veritaserum.