Necromancing the Stone - S5-E21
Visible crew/equipment: After Phoebe tells Jason that she'll go with him to Hong Kong in the morning, when it cuts to Piper and Paige looking out of the attic window, the reflection of a crew member is visible in the window behind the candles. (00:33:40)
Necromancing the Stone - S5-E21
Plot hole: Piper mentions that Grams banished the Necromancer "sixty years ago" at Patty's Wiccanning. Grams soon thereafter says that the Necromancer has had "almost seventy years" to regain his strength. However, Patty was born in 1950, and this episode aired on 5/4/03, at which time Patty's Wiccanning could not have been more than 53 years earlier.
Necromancing the Stone - S5-E21
Visible crew/equipment: When Piper hits the mirror after being thrown across the room by the energy bolt, look closely at the roof in the other room: a black rectangular hole with a stage light poking out of it is visible.
Visible crew/equipment: After Leo leaves Piper alone at Darryl's party in the park, when it cuts to Elise and Phoebe at P3, we can see the two T-marks on the floor behind them when they walk over to the counter. (00:12:35)
Continuity mistake: In 3-5 Sight Unseen, we can clearly see Cole turn the air conditioning very cold and open all the windows so that the Prue, Piper and Phoebe can see the invisible demon, and in season 2 when Prue is turned into a man Phoebe asks "did you fix the air conditioning?" But in this episode Phoebe asks Piper why they have never invested in air conditioning.
Answer: "Hush, Hush, Hush" Paula Cole.