In episode Death Become Them Piper wanted to cancel Chris's first birthday much to Leo's dismay because Zankou wanted to kill the family. She said "he is only one, he won't be remember" and Leo replies "we will" Here, Leo uses the same expression although he says that "Wyatt is not three yet and he won't remember Halloween".
Dogan's extended fingertips seem to not be the same color as his real skin - they appear fake.
In previous episodes, vanquishing potions are shown only to explode when they hit the demon they were made for. If they miss their target, they simply spill onto the floor. In this episode, however, a potion is shown exploding when it hits a wall.
During this episode Billie never mentions that it's strange seeing the real Charmed Ones. Tecnically Billie knew the characters of the three cousins, she didn't see the real appearance of the Charmed Ones. So why did Billie ever say something about the new look of the sisters?
When Paige shows the reporters around the Manor, she takes them to the attic and mentions that their Grams' sewing machine is broken. This could be refering to the episode Look Who's Barking, when Piper blew it up by accident.
TRIVIA: This episode features a spell to erase painful memories - "After this cruel memory is seen and said, erase these thoughts from my heart and my head."
Paige says to the journalists that they are the third generation to own the Manor. The three generations she's referring to are themselves, Penny & Allen and as mentioned in the season 2 episode Pardon My Past, the Manor already belonged to Penny's parents (although their family name isn't Halliwell, but Baxter for the mother and Johnson for the father). While upon hearing this one may get confused and think the show was mistaken and it was four generations it was not! Patty died when the girls were very young and therefore never inherited the house causing ownership to go from Grams to the girls.
TRIVIA: In this episode Piper's costume is a mouse, Paige's is an angel, and baby Chris is a wizard.
TRIVIA: This is the 2nd marriage and divorce for Phoebe; the first being to Cole Turner who was a demon posing as a lawyer.
TRIVIA: This is the second time Halloween is celebrated, the first time being in the season three episode: "All Halliwell's Eve".
When Leo and Piper are having their spat in the bedroom after Leo's fight at Wyatt's preschool, the bruise on his cheek seems to disappear.
Phoebe: I'm pregnant.
Phoebe: No, this guy I met at the gas station - of course it was Dex!
Piper: We're screwed.
Billie (about vanquishing the Dogan): Please I know I can do this.
Piper: Fine, but if you get caught on tape I will vanquish you.
Billie(to Paige): She's serious?
Paige: Eh uh...just don't get caught.
Billie: No sombody's gotta take him down he's... he's killing other demons and gaining powers by the day.
Piper: Great. Witch vanquishes demon, film at 11.
Billie (about the jack-o-latern): Those things have always creeped me out.
Piper: You can fight demons, but you are afraid of pumpkins?
Billie: I'm not afraid of pumpkins!
Dogon (to his minion, after Billie almost vanquished him): Leave me! I've got a score to settle.
International Episode Titles: Italy: (Kill Billie: Vol 1) Germany: (Kill Billie: Vol 1) France: Le poids du passé (The Weight of the Past)
This episode got 4.32 million viewers.
The close-up of Billie's eyes, where they zoomed in and then showed the flashback scenes, was another allusion to the "Kill Bill" films.
Title: Kill Billie: Vol. 1
This is a reference to the Quentin Tarantino-directed film, Kill Bill: Vol. 1, starring Uma Thurman. The movie, released in 2003, was followed up by the 2004 sequel or second half, Kill Bill: Vol. 2. The series then followed up this episode with Kill Billie: Vol. 2.