New Theory about Why Sirius Played Trick on Snape

[finwitch]

No: HPFGUIDX 33859

Very good! - Snape as a werewolf... How would Sirius - anyone- make 
sure Snape doesn't tell Remus is werewolf? Make Snape a werewolf, too! 
And, yes... It would be just perfect! Can't beat 'em - join 'em. But 
even better: make 'em join you!

What if Snape's a werewolf? He CAN brew Wolfsbane potion himself that 
no one notices, he knows about Whomping Willow...