The Twits by Roald Dahl.
Mr and Mrs Twit are the most horrible couple imaginable. Mr Twit has a filthy, food-caked beard; Mrs Twit has a glass eye that she uses to spy on her husband. They play disgusting pranks on each other constantly — each trying to outdo the other in nastiness. They also keep a family of monkeys in a cage and make them practise standing on their heads.
The caged monkeys — the Muggle-Wumps — communicate with the Roly-Poly Bird, who brings their plan to escape. The birds fly south for winter but promise to come back and help.
The Muggle-Wumps and the birds carry out a spectacular revenge: they glue all the Twits' furniture to the ceiling while the couple are out, making the house look upside-down. When Mr and Mrs Twit come home, they believe the world has turned the right way up and that they must stand on their heads. They are glued to the floor and slowly get 'The Shrinks' — shrinking away to nothing.