A boy mad scientist isn't mad in a bad way. He knows the girl he wants is above his social status, so he develops a way to make her not care about money or status and choose him.
Ray with casted hands finds his sister a willing participant in allowing him to release his pent-up spunk. He reciprocates by eating not only her cunt but her ass as well. As they are going at it, mom catches them. Instead of a scolding, she finally joins them in the taboo act of family incest.