Connections

First the shower scene quotes the shower scene in psycho, and then later the "killer" has what is supposed to be his dead grandmother stored in the basement.

Dr. Friedkin shares his surname with William Friedkin, the director of the Exorcist.

Jack is referred to as "Paddington".

Jack refers to a woman at the launderette as "Caligula".

A character says 'Say hello to my bowie knife'.