At one point, William H. Macy's character says "Fuck you, fuck the lot of you, fuck you all!". Director David Mamet previously used this line in the film "Glengarry Glen Ross (it was shouted by Ed Harris's character).
The trivia items below may give away important plot points.
The philosophical dialog about consciousness and dogs between Edmond and his cellmate that takes place at the end in their prison cell is based on a science fiction theory about the origins of dogs and the canine star Sirius. The theory postulates that dogs came to earth from Sirius and that they were bipedal and were able to speak, but upon arriving here, humans enslaved them, forced them to walk on all fours and made them forget the power of speech.
The number 115 comes up numerous times in the film: In the beginning as an appointment time of 1:15 for Edmond, 115 is the address of the tarot reader's shop Edmond goes into, 115 is the number of Edmond's cell when he goes to prison.