The deal is that the guy's wife was told to abstain from sex for a while after she got pregnant. So, the dude and his son decided to work together to find a way for him to masturbate in a way that would simulate her vagina until he could fuck her again.
"The Shubins “would sit around the table and talk about how we thought it should look,” Shubin remembers. “We were a pretty open family.”
Was he like "Son, do you think this would feel more like your stepmom's vagina? Or should we tighten it up a bit?"