The designers who created Buckbeak studied mythical depictions of Hippogriffs, in addition to real birds, such as the golden eagle. They even conferred with veterinarians to be sure Buckbeak's proportions were realistic!
Production designer Stuart Craig says the Gryffindor boys' dormitory was deliberately small to show that it was a cozy and comforting space for Harry, "which contrasted with the vastness of the rest of the space."
"If you look at the detail of the hut, you see that it's decorated with little animals all around, and you get the feeling some real animals might be under the bed!" - Production designer Stuart Craig, on Hagrid's hut
Each of the 17,000 boxes in Ollivander's shop was affixed with a label and then aged and overlaid with dust to create the look of having sat in the shop for a very long time. Take a look in #DiagonAlley!
Buckbeak had high-maintenance hair! The model was coated in glue, given an electrical charge, and then covered with oppositely-charged hairs. During filming, the crew had 40 minutes to brush it in place before the glue dried or they'd have to start over!