This is one of the best parts of the story. The raw desire for Lincoln to take Rita with such fervor. We've already seen how their mutual desires flared while the matriarch was disguised, now we get to see its purity. Lincoln's lust towards his mother, needing to dominate and fulfill the fantasy that plagued his mind for so long as Rita's body dared to entice him. Rita, being the matriarch, taking responsibility for her son's pent up needs and allowing her body to feel his love, while demonstrating her desires to the younger lad. For the moment, it is just the love of a mother and son. Lori and Leni watch it in its beauty, yet eager to be involved. Just a few more pages and we'll see its magnificence.