40 Creepy Facts About The Black / Lestrange Family From Harry Potter
In the Books, Sirius Can Transform Into a Huge Dog
In both the books and the movies, Sirius is an animagus. It’s one of the reasons it’s so hard for people to find him after he escapes Azkaban — he never was registered for shapeshifting into an animal. He turns into a dog in both the books and movies too. In the books, though, the dog that he turns into is quite large. It’s described to be the size of a bear.
The movies elected to simplify Sirius’s transformation by turning him into a normal-sized dog. This allowed them to cast real dogs, instead of using CGI, which may have proved difficult. If Sirius had been bigger in the movies, though, he might have done a better job going head-to-head with a werewolf.