The bear owned by the gypsies was actually recycled animation from A Bússola de Ouro (2007). The Polar Bear was changed into a Grizzly for this movie.
Inspector Francis Aberline (Hugo Weaving) was based on Frederick Abberline, a Scotland Yard Inspector that investigated London's Jack the Ripper murders in 1888. This fantasy version of him very much resembles the one in Do Inferno (2001).
Producer and star Benicio Del Toro is a huge fan of The Wolf Man (1941), and remained attached to the remake ever since it was first announced in 2006, and passed through the hands of several directors.
When the Wolfman is being chased in London, he jumps off of a building and lands on a policeman. This was accomplished with real actors and stuntmen, and not CGI.
The way Sir John Talbot (Sir Anthony Hopkins) plays the harmonica while walking through the halls of the asylum, was Hopkins' idea.
Rick Baker: The make-up artist appears as the gypsy man who whistles, prior to the werewolf attack on the gypsy camp.
Max von Sydow: Seen only in the Director's Cut in an uncredited cameo, he played a character who says he purchased the silver-headed cane at Gevaudan "lifetimes ago". Gevaudan (a French county now renamed Lozere) was famous for a series of attacks on humans in the 1760s, attributed to a werewolf-like "Beast of Gevaudan", elaborated on in O Pacto dos Lobos (2001).