The original title of the episode The Initiative was ‘Secret Agent Man’, but it was felt that this would give away Riley’s secret identity too easily.

The Initiative lab (in which Spike is kept caged in The Initiative) is actually a very small set, made to look bigger using mirrors. You can see at the beginning of the episode that the corridor is very long, but when Spike escapes, it’s only very short.

The Initiative set is at a place called “Skunk Works” which is about an hour south of L.A. The building used to be the location where stealth bombers were built. The big white balls on the main Initiative set are both an homage to 60s cult TV show The Prisoner …

Spike looks at a list of Stevenson Hall residents in The Initiative. The names are those of people who worked for Buffy, including Jeff Pruitt (stunt co-ordinator), David Solomon (co-producer), J. D. Peralta (assistant to Marti Noxon), Cindy Rosenthal (Costumer), Victoria Rushkin (set designer) and Lisa Rosenberg (hair stylist).

The t-shirt that Oz is wearing at the Bronze in Wild at Heart when Veruca’s band is playing has two Chinese characters which read (in Japanese) as “taihen” meaning ‘terrible’.
On the DVD for the episode, there is a running commentary by Joss Whedon, Marti Noxon, and Seth Green, and …

James Marsters (Spike) was uncredited in the original airing of The Harsh Light of Day but was later added to the opening credits. This was so not to spoil the surprise of his character’s reappearance.

The explosion scene in Graduation Day (Part 2) was filmed at 5am in Torrance, California (where the show had been filmed for outdoor scenes the past three years). The sound and vibrations from the exploding set woke up many residents and set off car alarms, causing locals to ban any …

The Mutant Enemy monster is sporting a graduation cap at the end of the episode Graduation Day (Part 2).

In Graduation Day (Part 1), Cordelia complains that she wanted the graduation robes to be teal and not maroon in colour. In the original script, she wanted the red but the school went with the blue.

Angel dreams that he and Buffy get married in The Prom. A photo of Buffy and Angel in their wedding outfits appeared in TV Guide before the episode aired, leading to fan hysteria that the two would marry.

Buffy’s wedding dress in the episode The Prom was designed by Vera Wang. In real life Sarah Michelle Gellar’s wedding dress for when she got married to Freddie Prinze Jnr. was also designed by Vera Wang. Buffy’s pink prom dress was designed by Pamela Dennis.

The Sunnydale High School clocktower was constructed especially for the episode Earshot.

Buffy’s class discuss Shakespeare’s Othello in the episode Earshot. In the original script, they discussed Henry VIII (you can still see this written on the board later in the episode) but Joss Whedon rewrote the scene to make it have more meaning to Buffy’s feelings.

In the season four DVD commentary for Wild at Heart, Seth Green, Joss Whedon, and Marti Noxon mention the frequent appearances of the extra they call “Asian Dan”. He can also be seen in the episode Earshot.

A line of Wesley’s in Enemies, cut for length was, “You failed in last night’s mission because you lacked faith. If you had simply…’Lacked Faith.’ A pun. From me! Bet you never thought I had the funny in me, eh?”