Halloween in COS

[greatlit2003]

No: HPFGUIDX 53686

I noticed something unusual in the scene in Lockhart's office on 
Halloween in COS, when Mrs. Norris was petrified. Dumbledore and 
McGonagall were trying to revive the cat, but Snape just stood 
there, not saying a word, and trying not to smile. This is not at 
all consistent with his behavior in other books, because we know 
that he is a take-charge type of person. He is never so passive. Why 
was he smiling?

"greatlit2003"