Why do my testicles move out of my scrotum and then back in again and why is my scrotum hard sometimes?

This is due to the installation and the case with very many. The Kremaster reflex ensures in all situations that the testicles are used to the body. This also includes the highest excitation phase in orgasm; often also the time before and after. If the testicles are already close to the body in the testicle bag (because it is often referred to as a “sport bag”, rather tight and short, than slack and long; the latter is often referred to as a “hanger”), and the “sport bag” still comes to the installation of a rather wide semen guide channel, then the testicles slide in such situations into the bar bow, where they can hardly be at all. Don’t worry: you come out and down from there regularly.

The same reflex also ensures that the scrotum feels hard in such and other situations.

This reflex is e.g. also caused by anxiety, stress, severe physical stress and cold. It’s all normal.