Bro,
It was piss and her cum mixed up its very rare that women actually just cum, cum.
Ok this can be triggerd normally by stimulation of the clit now every woman will do this if the orgasm is powerfull and intense enough. also if you hit the g-spot and the clit at the same time this will normally happen.
However the best way to get to it is once your gilr has come if she can take it keep hammering her clit it will be quite harsh for her but another orgasm will follow and that one will normally do it.
Also make her cum but not cum hard so you dont push her so it gets to sensitive on her clit then take her there again she will cum not very hard, each time you make her go it will get more intense by the time you hit about 4 to 6 she will have a big one when this happens hammer that clit as hard as you can and wham ejaclutate she will.
Its quite a turn on watching a woman squerm..!
Tip you know when your doin it rite as her chest will get all red and blotchy this happens when women have multiple orgsums and is normal.