S. Snape suspected snake speech?

[MMMfanfic at hotmail.com]

No: HPFGUIDX 16814

The duelling club scene was right after Harry blew up Snape's 
classroom.  Harry said that Snape knew it was him and would find 
some 'foul' way to get him.  It's entirely possible and in character 
for Snape to accidentally let the whole school knows that Harry is a 
Parseltongue. (like Lupin's condition -- see the pattern emerging?)  

Of course, it could well be a coincidence -- JKR has to put the 
discovery in somewhere.  But since it's JKR, I doubt it.

The question (if Snape knew beforehand): How did Snape know Harry is 
a Parselmouth?  Did Dumbledore told him or is it something else?

The question (if Snape didn't knew): Given the amount of time he 
spent with the other parselmouth, wouldn't he be at least slightly 
pale or surprised at the discovery of another one?

Also notice how expelliarum has fast-becoming the all-purpose, all 
occassion spell for Harry?  Attack by a giant spider or an evil dark 
lord or a phantom from a diary or a half-wit DADA professor or an 
unbalanced Potions Master? Expelliarum!  Expelliarum!
My question is: Why did JKR get Snape to teach Harry the most useful 
spell in the book?  Is it significant that Harry is unusually good at 
the disarming spell?  Is a cigar just a cigar?