Both D’Hoffryn and Spike say, “From beneath you it devours” in Selfless, a reference to the coming evil first mentioned in Beneath You.

In Selfless, Anya says to Buffy, “Are there any of your friends you haven’t tried to kill?” Buffy tried to kill Xander, Tara, Willow and Dawn in Normal Again; Spike on several occasions; Willow in Grave; Faith in Graduation Day (Part 1); Angel in Becoming… Need I go on?

In Selfless, Spike says that Drusilla liked to look at the stars. We saw her doing this in Innocence:
Drusilla: “I’m naming all the stars.”
Spike: “You can’t see the stars, love. That’s the ceiling. Also, it’s day.”
Drusilla: “I can see them. But I’ve named them all the same name. And there’s …

In Amends, the First as Jenny says, “I wanna die in bed surrounded by fat grandchildren, but guess that’s off the menu.” In Chosen, Buffy tells Angel, “No I don’t see fat grandchildren in the offing with Spike.”

The end sequence of Forever is very similar to W.W. Jacobs’s short story The Monkey’s Paw. In the story, the wife (Dawn) wishes (casts a spell to bring) her son (mother) back from the dead, he (she) appeares at the door, wife (Buffy) rushes down and throws open the door, …

When Buffy’s co-worker is showing her how to work on the grill, we see that he’s wearing plastic gloves. Then he puts two beef patties on the grill and he suddenly isn’t wearing gloves. In the next shot there are now four burgers on the grill and he’s wearing gloves …

At the beginning of Bargaining, the camera pans up to Willow, who is on top of a crypt in the graveyard. You can see what seems to be a part of the camera on the very right of the screen

As Buffy is fighting the newly-risen vampires in the basement, she stakes the vamp in the blue shirt on the wrong side of his chest.

When Buffy, Willow and Angel are on the roof of City Hall, Buffy hands Willow a book to begin her spell. You can see that she opens the book twice in different shots.

When Spike and Anya fight in the Bronze, Anya throws Spike onto the pool table and the front panel of the table falls off, revealing pale wood. In the next shot of Spike on the table, the original dark panel has been replaced.

The heels on Buffy’s boots change at the end of the episode Chosen. When she runs up the stairs to escape the destroyed hellmouth, the boots have high heels but when she jumps off the bus at the end of the episode, they’re much lower. Only Buffy would change her …

Anya’s song ‘Mrs’ is sung in Selfless. The lyrics are:

Mr. Xander Harris. That’s what he is to the world outside.
That’s the name he carries with pride.
I’m just lately Anya.
Not very much to the world, I know.
All these years with nothing to show.
I’ve boned a troll, I’ve …

Anya wears her wedding dress from Hell’s Bells in her musical-based flashback in Selfless, implying that she brought her wedding dress long before her wedding day in season six.

In Selfless, we see a flashback to a night that obviously is intended to have taken place during the musical Once More, With Feeling, on the first night that everyone began singing. Anya asks Xander if the coconut thing was weird. In the musical she told the gang, “We were …

The 1905 scene set in St. Petersburg in Selfless was originally supposed to be set during the Renaissance but it was changed as the time frame clashed with the fact that Halfrek was supposed to be Spike’s first crush Cecily at that time (seen in Fool For Love).