She kisses you.

The kiss takes you by surprise, and you smile, right before post-orgasm clarity kicks in, and you realize what you did.

"Uhh, mom, what did we do?" You ask, your eyes wide.

"Well, I just helped out my son." She giggles as she looks at the cum. To your surprise (although, with what just happened, it really shouldn't have been.), she scoops up the cum from the floor, and rubs it all over her breasts and arms, almost like a moisturizer. "And we shouldn't waste your seed."

You watch her, strangely turned on by this odd behavior. You're about to open your mouth, when you feel the aura again.