Continuity mistake: Near the end, when Elizabeth and her mother are having wine, in one shot her mother has put the glass down on the table, but in the next shot, from behind her, she has the glass in her hand again. There was no time for the change.
Continuity mistake: When Cleo and Mark are playing basketball, when Mark shoots for the first time Cleo is standing to the left of the hoop - when the ball hits the rim it launches off the rim to the right, but in the next shot Cleo has the ball.
Continuity mistake: When Abby gets bitten she holds her wrist but in the next shot her hand is covering her upper forearm.
Answer: It was in "Chaos Theory", the first episode of season 9 (time code 00:13:55).
Super Grover ★