The scorpion girl will attack using her stinger, if she lands the stinger attack three times, then the player is paralyzed and the sex scene begins.
In the sex scene, the paralysis removes the ability to get off. The scorpion girl rides you for a while until the poison wears off and the scorpion girl lets you finish.
Should the player submit to the scorpion girl then the sex scene does not include the use of her stinger at all. She instead opts to receive oral for a while, then quickly brings the player to orgasm and leaves.