The Chokey is a torture device featured in the book and film versions of Matilda.
Description and use
Closely resembling an iron maiden, the Chokey is designed to be narrow that no one can sit or squat while in it. Its measurement is said to be 10 inches and is filled with broken glass sticking out in the walls with nails on the door. The device was one of many dreaded my students as anyone imprisoned who tries to wobble will either be spiked by the glass or the nails.
Agatha Trunchbull uses this device during her tenure as principal of Crunchem Hall whenever the children break the rules. Hortensia states that students are kept in the Chokey all day. Once she leaves Crunchem Hall and disappears, the device was not employed again, likely converted to a closet to house the principal's coat and belongings.