Reprising his troll: ER star Abraham Benrubi once again plays Olaf the Troll - and, indeed, Anya's ninth-century ex-boyfriend, before she transformed him. He was first seen in season five's Triangle.

Sjornjost, 880 AD: No such place in Scandinavian or Baltic areas is known, and there's been much debate about which language Olaf and Aud's dialogue is in. The most likely intention is a parody of a badly-subtitled early film by Swedish maestro Ingmar Bergman, one of European cinema's most revered directors. Among his vast output are two 1950s films set in Medieval Sweden, The Seventh Seal and the Virgin Spring. The actors in Bergman's films would have been speaking modern Swedish, though Aud and Olaf appear to be speaking the same dialect as the Muppet Show's Swedish chef.

Kick his Ass: Goddard unfurls more fan credentials by referencing a loose end from Becoming Part 2. When Xander argues with Buffy about the need to kill Anya, Buffy reminds them fiercely about having to kill Angel in that season two finale. "Do you remember giving me Willow's message: Kick his ass." Xander - with his own agenda on Angel - lied about the message. He should have said Willow was progressing a restoration spell. It's probable that, in raising this, Goddard was aware of the intense debates between fans over Xander's actions after Becoming. Anyway, from Willow's perplexed reaction, it looks like the three have never discussed the matter since.

Better than Freon: Xander would rather help Buffy to track the Crimslaw spider demon "than breathe freon for eight hours" on his construction site. A trademarked 'miracle compound', Freon was invented in 1928 by Thomas Midgley, Jr. aided by Charles Kettering. Its chlorofluorocarbons, or CFCs, were used for several decades in refrigeration and aerosols. CFCs have since become infamous for worsening the damage to the Earth's ozone layer. Midgley went on to invent leaded petrol - another major pollutant in the making.

The revolution starts here: Anya and Halfrek are seen in St. Petersburg, basking in the chaos of the Russian Revolution of 1905, unleashed by Anya herself. Anya confidently predicts "a victorious communist revolution", contrasting hugely with her usual cheer-leading for capitalism. The thing is, although there was much turmoil in Russia throughout that year, the Communists only seized control much later, during the turmoil of the Great War in 1917.

I Am The Law: Buffy's outlook on her calling has hardened considerably since Consequences, where she disputed Faith's claim "We don't need the law - we are the law". Now Buffy has adopted Judge Dredd's catchphrase for herself. The Mega-City lawman's phrase has been used as a song title by both the Human League and Anthrax.

Mrs Harris: Anya's song, a new flashback to the events of Once More With Feeling, was written for Selfless by Joss Whedon. Drew Goddard told the Bronze Beta board that Whedon pretty much wrote the number overnight.

"It�s called 'Mrs'. I can't take any credit for it whatsoever. We were on the set of Firefly when Joss was directing (that series' premiere) The Train Job. He said something like, 'What if we flash back to the musical�' The very next morning he walked in and said, 'I've got the song.' Sometimes I think you can start car batteries with his brain."

Within the lyrics, Anya adds Xander's surname, Harris, to the full name she claimed to have in Checkpoint: Anya Christina Emmanuella Jenkins.

Vengeance denied: Selfless marks Anya's second farewell to vengeance with a recurring character's exit. It's a scorching goodbye to Kali Rocha, making her sixth appearance as Anya's goading fellow demon Halfrek.

From beneath you, it devours: Ooh look, there's that phrase again, and D'Hoffryn's using it. Wonder what it really means?