When Phoebe and Paige revisit Piper and Leo's wedding, at some point Cole asks past Phoebe if she's ok. (To which she lightly responds "Oh yes.) This snippet was not present in the season 3 episode "Just Harried" from which this particular flashback came from and is likely extra footage that did not air.
The Familiars entry in The Book of Shadows reads, "Familiars are enchanted creatures who follow and guide new witches to protect them while they learn the Craft. While they are often cats, other animals, like dogs, rabbits, horses, and snakes can be familiars as well. Familiars are naturally attuned to this seasons and phases of the moon and can be helpful in teaching the young witch a heightened awareness of her environment".
Throughout the series Kit the cat was referred to as a male, but in the episode "Cat House" we find out that Kit is in fact a female.
In the flashback that shows Piper telling Leo she loves him from season 1, it shows Piper and Leo orb out of the attic at the end of the scene. In the original scene they don't orb but just walk downstairs.
The house used in the beginning of this episode (Kit's house) is the same house that David Silver lives in on later episodes of Beverly Hills, 90210.