Melting can follow many pathways Melting involves the loss of order as additional kinetic energy is added to a system. Although simple models of this sort of phase transition exist, it can be very difficult to observe the initial stages either experimentally or using simulations. Samanta et al. developed a robust rareevent sampling technique that makes it possible to examine melting events without needing excessive computing time (see the Perspective by van de Walle). For both copper and aluminum, they observed the formation of defects that act as starting points for the melting process rather than the homogeneous loss of order assumed in classic nucleation theory. Science , this issue p. 729