What's this about? I'm surprised Harry didn't immediately jump to suspecting Snape was somehow involved in the attack.

I'm not really a major HP fan (I've read all the books at this point, but I'm not really into the whole deal) but when I read that, I thought that Snape was simply amused that Mrs. Norris had been attacked. There's some ongoing conflict between Snape and Filch, isn't there?