1. Why didn't that kid lock the door? If he felt like he needed to have some privacy then he should've found a way to keep his mom/dad/sibling out.
2. That is one accepting mother. That's kinda rare to find in the 1970's. I thought many were intolerant against such acts of pleasure.
3. How did his mother know instantly that he was masturbating? That kid really didn't make any major movements that could be shown as jacking off, plus he was doing it under his sheets.
4. Did he not hear his mother come in? If I heard footsteps while I was masturbating and had my door unlocked, then I would probably stop when she would come in.
Maybe I'm overanalyzing, but that's some messed up stuff right there.