Continuity mistake: After Winifred, Sarah, and Mary get off the bus, when the young girl dressed as an angel stops and says, "Bless you," the candy bag she's holding switches from her left hand to her right arm, then back to her left hand, between shots. (00:48:10)
Continuity mistake: When the parents are at the party, Dani and Max's mother puts her hands up while she is dancing and you can see her wedding ring in the shots facing her, but in the shots facing Dani the ring is gone. (00:55:20)
Answer: They were set up, beforehand, just in case. Winnifred knew about the spell, but she didn't memorize the incantation. So she needed the book to see how to cast it.
Phixius ★
If you pause the movie, you will see that the book opened up to the Black Flame Candle spell.