Faith's line, where she offers a theory why the blind Bringers are so good in battle, was cut: They say your other senses get better. Maybe all blind people are smokin' in a knife fight... Not saying it's likely.
Caleb's line to Xander that he "sees everything" references Xander's conversation with Dawn in Potential (2003), in which Xander said "I see more than anybody realizes because nobody's watching me."
Nathan Fillion was the star of Joss Whedon's cult phenomenon, Firefly, which was cancelled after just one season. With news of the cancellation, he offered many of the Firefly cast guest starring roles on his other shows. Nathan Fillion as Caleb, Gina Torres went to Angel as the season 4 villain, and Adam Baldwin guest starred on Angel in season 5 as an adversary.
Faith tells Willow that she has spent too much time in hospitals. She is referring to her eight-month-long coma, spanning from Graduation Day: Part 2 (1999) to This Year's Girl (2000).
Faith recognizes Spike, but Spike thinks they've never met. In the episode "Who Are You?", Faith met Spike for the first time while inhabiting Buffy's body. Spike then reveals that Buffy filled him on the body swap eventually.