One of only three shows to take place on Halloween. They take place in Season 2, Season 4, and Season 6.
Spike's admonishment of the vampires for not taking off for Halloween can be seen as a bit hypocritical. In season two's Halloween (1997), he attempted to kill Buffy during the chaos caused by Ethan Rayne. This may also be the reason for his warning, as he did not succeed.
When asked to get more Mandrake Root from the basement, Buffy comments that it won't be her fault if they "have this conversation over and over" and over again, a reference to the time loop in the previous episode, Life Serial (2001).
Xander misquotes a line from Shakespeare's play, Henry V (1599): "So, one more into the breach?". The line is actually: "Once more unto the breach".
Spike says: "Great Pumpkin's on in twenty." He's referring to Charles Schultz's animated Peanuts Halloween special "It's the Great Pumpkin, Charlie Brown" (1966).