From this interview with Del Toro:
http://www.aintitcool.com/node/50956"I thought they came out really great. In an oblique way, I set up the movie in Lovecraft territory, because I think in an oblique way the characters are also an homage to “Dreams in the Witch House”, a short story by Lovecraft that has a character who has the body of a rat and the face of a man. There’s this little character called Brown Jenkins, who is really, really creepy."