Pressing firmly on the vagina and not letting her cum, the sex naturally continues. Just as she starts to feel good and is about to naturally climax, he "forcibly stops" her. Like how we men grip our dicks tightly right before ejaculation to stop it, the pent-up orgasm that has nowhere to go gets charged up, and just as she's about to reach an even bigger climax, he repeatedly and forcibly stops her with "No, you can't cum yet!" When the pussy is completely out of its mind and at its limit, and he finally says "Okay, cum now," just watch—she'll explode.