Any stimulation of the anterior and/or posterior walls of the vagina is liable to being this condition on. Personally I'm convinced it originated from assisting in childbirth from long long long ago. The fact is the ejac can happen separate to/from an orgasm butt of course combining the two is the aim most times. It also happens all the time with some, some of the time with many and never for the others. NO IDEA WHY that happens time of the month, stress, diet, sleep cycles .