Trivia: The actor who plays Nicholas Brendan's evil twin in "The Replacement" is actually his real life twin, Kelly Donovan. Both the brothers use their middle names when working rather than their real surname, Schultz.
Trivia: In 'The Replacement' Xander says to Willow 'Let's see how well you handle it when there's an evil version of you running around.'. Willow's reply, 'I handled it just fine,' is a reference to the episode 'Doppelgangland' from the previous season.
Trivia: In the episode 'The Replacement' Buffy asks what they're going to do with the 2 Xanders who then say 'Kill us both Spock'. This is a reference to an episode of Star Trek where Kirk ended up with an evil twin and Spock didn't know which one to kill, the real Kirk told Spock to kill them both so Spock killed the other one.
Trivia: In the episode 'The Replacement' when Xander is trying to convince Willow that he is the real Xander, he does the Snoopy dance for her. Nicholas Brendon didn't know what the snoopy dance looked like and just attempted it after a brief description. He is now frequently asked to perform it at any fan conventions he attends.
Chosen answer: Angel is saying that he is still jealous and Buffy recognizes that this is his way of saying he wishes that they could be together. That is why they both smile.