Kacper lives in a block by the park. He has a red backpack with a big lock. He doesn't seem to speak, but sometimes he mutters. Today Kacper packs crayons, a sandwich and a ball. Mum calls out: "Hurry up, you're going to be late!" Kacper zips up Ziu and runs to school. In the corridor Ziu quietly and strangely grunts. Kacper whispers into his backpack: "Ziu, is that you?" The backpack replies very quietly: "My stomach is burping". "Don't eat my sandwich!" asks Kacper bewildered. "I don't want a sandwich," mutters Ziu. "I want crayons." In the classroom, Ziu gasps and rustles happily. Mrs Basia is writing a topic on the blackboard. Suddenly a crayon jumps out of his backpack and dances. The other crayon takes a leap and says: "Hey!" The whole class giggles, even the lady laughs. But Ziu suddenly gets big and round. The lock shakes like a drum and glows green. Kacper looks wide-eyed and asks in a whisper: "What's up?" A sound comes from Ziu: "Yummy, yummy.... another one!" The backpack jumps up, spins around, and suddenly silence breaks. The zipper slowly opens, and inside....