A couple of OotP puzzles for me

[cubfanbudwoman]

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I really thought that Yates & Goldenberg by and large did an amazing 
job of cutting out things which made *sense* to cut out.  Taking 
what was the longest book and turning it into the shortest movie 
seemed impossible, but they did a nice job, I thought, of figuring 
out what was logical to remove or tweak.

On the other hand, what struck me in a couple of places was what 
they elected to leave IN, given the things they had elected to take 
OUT.  

For example:

(1) Why leave so much Grawp in, including his being struck by a 
centaur's arrow & then pulling it out -- all of which mattered in 
the book because the blood from that drew the thestrals -- but that 
part of the story wasn't even used in the movie.  
(2) While the Weasley fireworks were delightful (hee), they didn't 
quite make sense without Umbridge's Quidditch ban/broom lockdown & 
Harry's need for a distraction in order to speak with Sirius about 
his concerns about James after the Snape pensieve incident.  Since 
they dispensed w/ Quidditch altogether; melded the pensieve memory 
into the Protego-caused look into Snape's mind; and didn't have 
Harry ask Sirius about James' behavior; there really wasn't much 
rationale for Fred & George's decision to depart, nor in that manner.

Anybody have ideas why they left these things in, given what was 
taken out that related?  

(I suspect the reason w/ the fireworks is just that they were funny 
& spectacular. :))

Also, why have Harry hear the prophecy *at* the DoM, rather than 
later, in DD's office?  Why cut the 'Big Talk in DD's Office' which 
is supposed to be Harry *really* angry and then DD *really* 
emotional as well?  As it came out, it was woefully brief and fairly 
emotionally flat.  

Just some things I'm about which I'm curious to have others' input.

Siriusly Snapey Susan