I read the first dozen or so pages of posts so I'm not sure if anyone has answered these queries yet. But:
1) In regards to Hermione saying she knows the Obliviate charm only in theory, yet she modified the memories of parents: Theres quite a few memory charms, not simply the Obliviate charm e.g. the confundus charm. I was always under the impression that Obliviate simply wiped a person of one or more of their memories, while there was another charm (never actually named) to implant new ones.
2) Ron's parseltounge: a pretty crummy plot device I'll admit. I assumed that he drew on the connection he had with the locket to say some paresltongue. It had a profound impact on him compared to the other two, and therefore he displayed some of Voldemorts traits: anger, suspicion etc. Parsletounge could be added to the list I spose.
And the epilouge cracked me up. SO CHEESY! The names were terrible. Harry is a sadistic parent to name a child Albus Severus. I'd sure as hell tease him. But I still loved the book. After the OoTP, this is my favourite. The epilogue couldve been heaps better if done differently. If it was like a year or two after the end of the book, and society was slowly rebuilding itself after the chaos of Voldemerts regime, struggling to put such violence and loss (particularly Harry's) behind them, i would've left the novels on a note of dignity. And if JKR writes some crap book about Harry's kids I'll shoot myslef.
I thought Hedwig's or Dobby's death were the saddest. They bothed loved Harry unconditionally and Hedwig was Harrys only connection to magic when he was at the Dursleys. Remus and Tonks death honestly didnt bother me. I thought their whole romantic relationship was so cliche.
Something my friend is really annoyed about is the invisibility cloak. According to the book its meant to be impenetrably invisible, yet Mad-Eye clearly sees Harry through it in book 4. have i missed something about it?
