Gunn says about the White Room, "Actually, it's not that bad... if you like cats." Angel nervously replies, "I'm kind of a dog person." It is part of TV lore that David Boreanaz was walking his dog one day when he was spotted by a talent manager and cast as Angel in Buffy the Vampire Slayer (1997).
This is the only episode of either series ever to have a viewer discretion advised warning in it.
Angel and Spike actually have the same first name. Spike's mortal name is William, and Angel's is Liam - the Irish derivation of William.
As Fred writes formulas on the windows, the others note that that's not a good sign, a reference to her previous habit last seen in Fredless (2001).
The sounds of the man in the basement chopping off his fingers were done by Foley artists chopping vegetables. In fact, they sound much more like carrots or cabbage than human fingers.