Just as Mr Jenkins is storming toward the witches' table, there is a terrible, loud shriek. All of a sudden, the GHW is standing on the table, waving her arms in the air.
Soon enough, all the witches are doing the exact same thing.
Then, all at once, they freeze in silence. Before you know it, they are transforming – into mice, shrinking, growing fur, the whole nine yards.
Our narrator is confused as to how it happened so quickly, but then Grandmamma reminds him that just like him, they'd all had an overdose (one bottle of the potion was good for making about 500 mice), and so the alarm-clock timing got messed up.
Just like that, all the witches are mice.
Cooks and waiters start running around with pans and knives, trying to kill the witch-mice. All the adults are screaming scared, but the children in the room seem to get the sense that something cool is happening. They all love it.
In all the commotion, Grandmamma brings Bruno back to his parents (not to his mom's delight) and heads outside to grab a taxi. She's leaving all of their luggage at the hotel and leaving town as quickly as possible.
The taxi driver notices the mouse, who Grandmamma plainly says is her grandson, and the taxi driver warns her that mice tend to breed really fast. Eek.
Grandmamma tells our narrator that they're heading back to Norway, and together, they soak in their victory.