Audio problem: When Miss Irvine is sitting the room alone after being ejected from the banquet, she says that she never wanted to be one of them but her mouth doesn't move. (01:17:31)
Other mistake: When the evil witches get their just desserts, Lois Leffour's friend Julia Whitman is choking on the Formula 86 bottle. Even though the bottle is small, Julia should have either seen it on the spoon, or felt it when she put it in her mouth. Instead, Julia swallows the bottle and coughs it up during her transformation into a mouse.
Other mistake: Before the Grand High Witch starts the meeting, Luke is watching the witches sit down, and he doesn't recognize the Woman in Black. This doesn't make sense because the Woman in Black attempted to kill him during the treehouse scene before any of them arrived at the hotel. The Woman in Black is even the first witch who tries to capture him when he runs on the stage.
Continuity mistake: When the evil witches start turning into mice, there is a close-up shot of the Woman in Black with mouse ears and whiskers, and her wig has fallen off. When the Grand High Witch is holding the spoon, there is a background shot of her dining room table, and the Woman in Black's wig is back on her head.
Continuity mistake: When Grandma says "Bruno's dad is about to have the soup", her right hand appears/disappears holding the bag depending on the shot.
Continuity mistake: After Grandma swings her closed bag in front of the Jenkins, angle cuts to a close-up of the bag and it's open.
Continuity mistake: Bruno's dad is about to have the soup and says "this is a nightmare", his wife is either holding the glass of wine or not, depending on the shot.
Continuity mistake: When Grandma says "Bruno's dad is about to have the soup" she is either holding the bag above the table, or the bag is resting on the table and her hand is gone.
Revealing mistake: When the mouse is pushing the potion down the spoon handle towards the soup, both the bottle and the spoon turn green due to the chroma screen.
Other mistake: When the Grand High Witch, the Woman in Black, and the other witches are counting down the seconds for Bruno's transformation, Luke temporarily steps out from behind the screen. Yet none of the witches in the front row notice him.
Answer: The potion was made for little children, not adults. It would have taken longer to go through their entire system.