Collective synchronisation occurs in nature when crickets start chirping in unison. In some parts of the world, fireflies blink on and off in perfect synchrony like a Christmas tree. The monthly cycles of women living together have also been known to synchronize.
Sorry, guys, that explanation won't fly. Ever since the Tacoma Narrows bridge in Washington state collapsed, natural frequency analysis has been part of any bridge design. And yet someone designs a footbridge with the natural frequency of people walking. Way to score an auto-goal on yourselves, chaps.