Wanking shrinkage

Q: Why do my testicles retract into my stomach when I masturbate??

A: Dear reader, while it can be disconcerting when any part of your body changes size without an obvious cause, this is nothing to worry about. It's usually just a sign of your body being very grateful for what you are doing to it.

Your testicles are actually little sacs of blood dangling in your scrotum. When you get en erection, the blood is pumped from these sacs to your penis. Hence your balls get smaller and your penis gets larger.

Note though that, if your balls ever end up becoming a vaccuum, despite the obviously impressive penis size you'll achieve, you do need to consult a medical professional.