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.
I worked at an office staffed mostly by women and there was a particular time each month that simply behooved having a ready supply of chocolate. When Sarah gets a little older the boys and I are going to have to have a monthly camping trip. But anyhow, the article is about bridges.