When Piper freezes the house while it is letting Andy leave, she also freezes Phoebe. However, Piper was outside, while Phoebe was inside, and it is established that Piper's freezing power doesn't work outside the room/area she is in.
After dinner, when Prue and Piper can't get back into the house, Prue is wearing a black band around her neck. The next morning she is wearing a gold chain and when the camera shot changes she is wearing the black band again.
When Prue and Piper are standing in the kitchen the stairs and the basement are pitch black. When they next walk down the stairs the steps and the walls are bathed in light.
After Phoebe vanquishes the Woogy, the whole house magically cleans itself, but at the end Piper, Phoebe, and Prue are cleaning it.
In the very first scene, we see the vase full of flowers from the hall table shatter due to the earthquake. Then, when the earthquake stops and the girls come down the stairs, Prue puts the flowers back into the vase which, instead of being shattered on the ground, has just fallen over, unbroken, on the table.
The house is stated to be a "spiritual nexus" equidistant between the five elements: earth, air, water, fire, and metal. This would be correct in Chinese mythology, but Wicca uses Air, Fire, Water, Earth, Aether (or Spirit).
When Prue and Piper are discussing Gram's Woogyman story and the events surrounding it, Prue describes it as the story of how to destroy it. However, the Woogyman was simply contained by Grams' spell. To destroy it required banishing the spiritual nexus itself.
The "gas man" would not have turned on a light in a basement that might possess a gas leak. He would have used a safety flashlight.
There are some errors in the credits. Richard McGonagle was playing the gas repair man, and Michael Mantell was playing one of the arguing neighbors, about 30 minutes into the show.
When the guest are about to relocate to Quake and they have discovered where Professor Whittlesey has been, she claims her time has been well spent and heads towards to door. When heading towards the door now visible you can see a crew member opening the door and leaving through it. The next shot shows the professor leaving the house with her hand on the door suggesting that she had just opened it herself.
The police car that Professor Whittlesey enters has a Los Angeles Police Department insignia on the door. However, the show is set in San Francisco.
Prue and Piper name five places that loosely correspond to the five elementals in order to find a pentagram in the map, but there are numerous places in San Francisco that could correspond to the five elementals. Furthermore any five random points on the map could be drawn as a pentagram.
Piper says that Twin peaks is the highest point of elevation in San Francisco, it's not, Mt. Davidson is.