Thanksgiving - S1-E9
Factual error: The scene where Kitty is making peanut butter celery for Thanksgiving appetizers; she is using Skippy brand peanut butter and the packaging is not from the 70's, it's the current packaging. (00:05:10 - 00:06:05)
A Paige from the Past - S4-E10
Factual error: On the wall of Paige's bedroom when she was a teenager is a Metallica poster for "Garage Inc.", a CD not released until 1998 although Piper later says that Paige has gone back to 1994. (00:16:05)
Factual error: Throughout this episode, when Carrie talks about the functions of the left vs. right sides of the brain, she has them backwards. The right side of the brain is the creative side, the left is the logical one. Apparently, the writers liked the idea that the "right" side of Carrie's brain would ultimately lead her to do the "right" thing about Mr. Big, but that's not the case. Rational decision are made with the brain's left side. (But then again, Carrie never was very rational when it came to Mr. Big.).
Suggested correction: The right and left side being rational/ logical and emotional has been proven wrong. The brain works in a very complex manner and multiple parts on both sides are lit/ functioning when doing either a logical or an emotional task.