Handedness, also called "chirality," is a directional property that physical systems may exhibit. A system is "right handed" if it twists in the direction in which the fingers of your right hand curl if your thumb is directed along the natural axis defined by the system. Most naturally occurring sugar molecules are right handed. Fundamental particles with spin also exhibit chirality. In this case, the twist is defined by the particle's spin, and the natural axis by the direction in which the particle is moving. Electrons produced in beta-decay are nearly always left handed.