Researchers studying flags blowin’ in the wind found that they behave unlike rigid bodies in an interesting way:
Often it pays not to be leader of the pack — just ask a racing cyclist or a Formula One driver. Conserving energy by following the leader, a trick known as slipstreaming, can give a rider or driver that extra bit of juice to pull ahead at the very last moment. In the natural world, however, bodies are more likely to be flexible, like a fish’s, rather than rigid, like a car’s. In these systems, as a recent paper in Physical Review Letters reports, it is the leader that enjoys a significant dynamic advantage over the followers.
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If one flag has a second downwind of it, that second breaks up the wake of the leader. This stops that wake being a single, coherent back-and-forth wave. As a result, the leading flag flies straighter. In a line of many flags, moreover, most experience this reduced drag in turn, making the whole group more aero- (or hydro-) dynamic.