During the filming of The Sorcerer’s Stone, Watson often brought her pet hamster to set. Sadly, it died a couple weeks into filming. The set department then created a specially made hamster coffin with velvet lining and “Millie” engraved at the top.
The two cousins never quite become best friends but “would still see each other enough to be on Christmas-card terms, but they would visit more out of a sense of duty and sit in silence so that their children could see their cousins,” according to Rowling.