Revealing mistake: When Ron is on all fours beginning to cough up slugs, Harry says "Let's take him to Hagrid's". Hermione mouths the lines with him. (00:39:43)
Suggested correction: No, she isn't.
Other mistake: In the ending credits, the character of Hannah Abbott is listed as "Hannah Hufflepuff."
Suggested correction: That is because the viewing audience (well in a deleted scene anyway) only heard her first name of Hannah and knew she was a Hufflepuff by her robes. This was done intentionally, not to say her last name is Hufflepuff, but so the audience would know who this is in reference to. Not everyone in the viewing audience is a die hard Harry Potter fan who would know that's Hannah Abbott with her last name not being said.
Plot hole: When Harry and Ron transform into Crabb and Goyle, he doesn't take off his glasses so then Malfoy can comment on them. Goyle doesn't need glasses - Harry's eyesight should've been immediately blurry, and he would have taken them off.
Suggested correction: For all we know Goyle does need glasses and either doesn't realise it or doesn't want to say it. When I was in high school for example, I used to give my glasses to students who couldn't read the board. They didn't wear glasses, but obviously should have had them if they could see better with mine. Plus it is shown from the film the potion Hermione made doesn't change things like internal voice boxes. It's reasonable to conclude it didn't work for eyesight either.
Other mistake: Harry now has Dudley's toy room and Dudley's is next to his, however when there is a shot outside the house there is only the one window on the left side of the house and not much space between it and the left outside wall, where is the window for Dudley's very narrow room? (00:09:00)
