Children can see muscles flex as a football is kicked, watch food travel through the digestive system as an apple is eaten, and take a peek at the skeleton holding a small boy upright while his height is measured. Sleep, dreaming, growing, and illness are also included, along with many other secrets of the human body. The unique design of the book allows children to discover a “hidden“ image by holding the page up to a bright light, or shining a torch behind the page.