When a baby will not stop crying, it can be frustrating. One well-known trick parents use is holding the child and walking around for a while. We are just now finding out why this trick works. It has to do with what happens in two different parts of the brain: the parasympathetic nervous system (PNS) and the cerebellum. The PNS is the brain’s relaxation command center. When babies are carried, the PNS relaxes their bodies (by dropping the heart rate), which gradually calms them down and stops their crying. Also, carrying triggers the cerebellum, which controls movement and makes the babies physically adjust, for example, by bending their legs to the person carrying them. Understanding how the brain works will teach us how to better soothe babies. In turn, the people taking care of the babies will be more relaxed, which will improve health, happiness, and parent–child relationships.