The phenomenon by which females become exponentially "girlier" when they congregate in larger and larger groups. This is thought to be caused by the increased availability of estrogen, the "female" hormone, within a given radius. Some hypothesize that ovaries serve a role in communicating with each other under such circumstances. It should be noted that Estrogen Amplification also occurs in post-menopausal women.
The loud, uncontrolled giggling in the office next to me is the tell-tale sign that 5 or more females are in the same room - surely, estrogen amplification has occurred.