When Willow and Tara are discussing Willow's increased use of magic, Willow uses a spell to mute everyone; "Sekaat", which is "Silence" in Arabic. Then, when Tara unmutes everyone she says "Takalam", which is "Talk" in Arabic.
One of only three shows to take place on Halloween.
Dawn and her friend joke about fooling their parents/Buffy by telling each of them that they're at the other's house, and they can't believe how stupid they were to fall for it. This mirrors Buffy telling Giles she was with her mother and telling her mother she was with Giles, when she was really with Angel - as well as the "round robin" that Buffy, Willow, and Xander all did during high school in order to cover demon research and fighting in Surprise (1998)).
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).