Plot hole: This episode takes place in 1967, and Penny (Grams) is married to a man named Allen Halliwell who dies in the episode. Allen is supposed to be Penny's "first husband," Patty's father and the Charmed Ones' grandfather. But it was previously established that Patty's father was named Jack, and he died in 1964.

Plot hole: Paige is sent back to when Grams was her age; this shows that they are family and that they share similar traits. Grams having orange hair is a mistake because Paige's hair is not naturally orange, therefore has nothing to do with genetics.

Plot hole: In the opening scene, Chris directs Piper and Phoebe on how to vanquish the amorphous demon. He says that it will attack "fast and hard" as soon as it senses Phoebe's magic when she levitates. But Chris had orbed out of the warehouse and back in, and the demon didn't react to the magic. Later in the episode, it is specifically attracted to a use of orbing, several times.

Continuity: In this episode, it's 1967 and Grams is young and unrecognizable compared to her older self. But in "That 70's Episode," it's 1975 and she looks just like she does today, not to mention that she has two grandchildren. Grams sure ages quickly...

Continuity: Robin falls over backwards after Paige dumps a cannister of marbles onto the floor. But Robin wasn't moving at all when this happened. Trying to walk over marbles will make you fall. Standing still while marbles roll around and bounce off your feet? Not so much.

Plot hole: When Piper and Phoebe appear in the past, Penny chides them not to "use [their] magic so openly." Immediately thereafter, Penny uses magic to turn some police officer's night sticks into flowers. That was some pretty open use of magic, right there.

Factual error: Phoebe, who has moved to Hong Kong, tells Paige that she, Paige, was born in the Year of the Ox. But Paige was born in 1977, the Year of the Snake. 1973 was the Year of the Ox.

Plot hole: After Paige changes the past, the ghost of Grams changes from a no-nonsense demon-hunter into a pacifist hippie. So, apparently, we are now in an alternate timeline where Grams never became assertive, and stayed a hippie all her life. The episode went to great lengths to establish that if Grams had stayed a hippie, she and the Charmed Ones would have all died young. But the ghost of Grams was still middle-aged, instead of decades younger, and Wyatt was still there, but he wouldn't have been if his mother Piper had died as a child.