1. In 'Harry Potter and the Prisoner of Azkaban (2004)', Hermione Granger (Emma Watson) urges the condemned Buckbeak, "Come and get the nice dead ferret" (when she and Harry Potter (Daniel Radcliffe) rescue the Hippogriff.
2. In 'Harry Potter and the Goblet of Fire (2005)', Draco Malfoy (Tom Felton) is briefly turned into a ferret.
3. In 'Harry Potter and the Deathly Hallows: Part 2 (2011)' (the "19 Years Later" segment), both James Sirius Potter (Will Dunn) and Albus Severus Potter (Arthur Bowen) have ferrets as pets/familiars.