Lenka and Kuba loved their walks in the forest together. Their favourite place was an old green tree with a hollow where a family of jays lived. One day, as they were walking along the path, Lenka stopped suddenly and whispered: - Can you hear it? There was a quiet, rhythmic clatter coming from far away. Cuba furrowed his brow and looked around. It was quiet all around, only the occasional rustling of leaves. - Maybe it's a woodpecker? - he suggested, but the clatter was different, as if someone was hitting a small box gently. The children decided to come closer. They passed the berry bushes, walked past a large anthill and climbed up a not-so-high hill. The closer they got to the tree, the louder the clatter became. Suddenly, behind the thick trunk of an old beech tree, they saw a mysterious box lying on the ground, and next to it.... Suddenly the bushes moved violently! Lenka and Kuba looked at each other with wide-open eyes. Would they dare to look behind the trunk? What will they find by the box?