What the actors knew or what we thought they knew

[potioncat]

Many of us grumble about changes from HP books to HP movies, although we understand there are differences between reading an event and watching that event. But sometimes it seems WB didn't really know what was going on--in the specific book or in the tales to come. Most of the actors claim to at least read the books--except for Gambon and Harris. 

I recall Robbie Coltrane saying that JKR had given him some background information. I remember in the interview he was joking that he wouldn't dare reveal what the information was. 

At one point during PoA filming Cauron said he wanted to put a graveyard scene in, but JKR told it was the wrong place. The graveyard comment gave us lots of grist for our mill over at main!

Dan talked about challenging JKR who said DD was giving her trouble in DH, and he pointed out that DD died in HBP. Seems she gave him a vague reply to that. After DH came out, Rickman was reported to say that he finally understood what was going on. 

But now that it's over...what could JKR have told RC that would be such a big secret? There wasn't any surprise about Hagrid. Was Rickman really in the dark about Snape? I'm beginning to wonder if the shrunken heads were the least of Cuaron's ideas and JKR had to pick her battles.

So I just wondered if anyone else had read things or given this any thought? What do we think the people knew?

Potioncat, hoping we haven't discussed this in the very recent past.