Why do birds flock? Shedding light on collective motions in heterogeneous populations

Electrifying plastic beads in a laboratory setup creates flocking behavior similar to that observed in birds. And if you mix beads of two sizes, they will automatically separate. This seemingly simple observation by Alexandre Morin and Samadarshi Maity teaches us about collective motion at all scales. "It's beautiful that something as complex as birds can be understood at its essence through beads."