I made a woman cum like that using only one finger, it's easy once you know which direction and amount of pressure to apply to her clit, every woman's clit is different and what she likes is different but once you know what she likes you can make her cum pretty quickly this way.
The woman I had an affair with did just that. She almost bit my tongue off and sratched my body all over. I wished she wasn't married. But you can't have it all.