There are many tricks a pregnant woman may use to try to commence labor: sex, spicy foods, exercise, and castor oil are just a few popular ones. During my last two doctor's appointments when my OB/GYN checked for centimeters dilated, she literally stirred things up. And by that, I mean she stripped my membranes. Presumably the action can fire up contractions and quickly send a woman into labor. In my case, it just hurt like hell and caused me to spot a bit and have contractions without the benefit of going into full blown labor. For some lucky mamas, it works like a charm.