Neighbours' Airbnb Guests

I didn’t see them the next day until the evening. I was doing my laundry when I heard noise in the backyard, near my back door. I opened the window slightly and saw someone fucking. “Young couple finding some quiet time for themselves away from the kids.” I thought, and decided not to disturb them. I went back into the flat to my study and turned on the security camera app, my voyeuristic desire to watch them fuck. Indeed, it was the son fucking his wife. She was lying on top of him, grinding her hips, while his hands grabbed her butts, pulling her into him. Their heads were hidden by the bushes but their moans were clearly captured by the security camera’s microphone. I didn’t understand what they were muttering, but I guessed it was sex talk. She was grinding and thrusting, working his cock inside her, until she suddenly froze. Her body shook for a while, very likely having an orgasm. After a while, they got up and switched position.