1.The scenes for 4 Privet Drive were originally shot on an actual street. They only ended up making houses because they didn't have access to the house for reshoots.
2.The graphics team hand-wrote thousand of letters but then found out that they were too heavy for the owls, so they had to make them again.
3.Even then it took the owls six months to learn how to carry them.
4.The doors at Gringotts actually work, it took three months to make the door they used for Bellatrix's vault.
5.There were over 20,000 packages and goods in the windows of Diagon Alley.
6.Crew members used ropes and wrenches to bend and twist the set once it was fully assembled to give it that whimsical look.