Bilirubin is formed when haemoglobin is broken down, and is basically the the pigment that makes faeces brown.
In The Silence of the Lambs, by Thomas Harris, Hannibal Lecter at one point says that the killer ‘Buffalo Bill’ is a former patient of his named Bill Rubin. In Harris’ previous book Red Dragon the killer Francis Dolorhyde had no teeth and was known as the Tooth Fairy.
Terry explains the name as follows:
“Oh, lor’. Billy Rubim is an old medical student joke…”
“Like most really stupid jokes, it’s one that you won’t spot unless you have the right background. Others on here will doubtless explain, but according to one of my informants, a nurse, every batch of medical students learns it anew and Mr Rubin’s name turns up in various places to general sniggering.”