Transference

“The true meaning of sex is to identify the right person to transfer our most intimate feelings, even when it leads to murder.”

The true meaning of sex is to identify the right person to transfer our most intimate feelings, even when it leads to murder. After all, the Mother is sleeping with her Son-in-Law, and the Daughter fully approves. It's a "who-done-it" and "why" that will leave the audience rethinking their own innermost needs for love.