wife always naked

My wife and I have been married for almost 4yrs and I have a step-son.  I always had dogs and at the time this happened we had 3 black labs.  My step-son would always called in one of our dogs named Blue to sleep in his bedroom with him at night.  One night I woke up cause I had to piss, on the way to the bathroom I heard what sounded like my step-son, and Blue was playing because I could hear Blue panting heavy.  So I was going to open the door to tell my step-son go to sleep it was late, when I opened the door I seen my step-son completely naked on his hands and knees with Blue was just drilling his asshole.  My step-son seen he trying to get Blue off him and he couldn’t because Blue’s knot was stuck in my step-son’s asshole.