Since balls seem to move on their own for no discernable reason, I was assuming maybe someone has noticed a correlation between tumescence (erectness if I didn't spell that right) and ball sack rigidness.
Actually there is no direct correlation between them. As it is the body regulating the proximity of the jewels to the torso in order to control the temperature of the testes at a constant 94°F. Your body essentially "incubates" your sperm and seminal fluid. This is an automatic (involuntary) function that humans have very little, if any control over. Mother nature does the temperature regulation, by raising or lowering the testes within the jewel sac... via contracting or relaxing the skin of the jewel sac. As the jewel sac contracts, the skin of the jewel sac thickens (aka: sac rigidness).
This process usually occurs only when the surrounding temperature is lower than 94°, as in when you go outside, when it's 45° out there, and it was 78° inside. Your loose gym shorts and no underwear soon has your body raising your jewels, and your jewel sac rigidness factor increases to keep those jewels nice and toasty at 94°.
Lets say you are tied to a cross, and your Domme slides your jewels into a baggy full of ice, and ties it on your jewels. What happens? The jewels get much closer to you as the jewel sac skin contracts. Pending internal blockage from injury, the jewel sac is capable of raising the jewel all the way up inside you, which would make the guy appear at a glance to be extremely jewel challenged (no balls).
Next time you take a shower, conduct an experiment. Set the water temperature to be comfortable, over 94° if tolerable, and dangle your jewels under the water. If the water is over 94°, your jewels will be lowered and your jewel sac skin appear to be very thin... a twofold purpose. 1- lowering the testes to allow cooling, and 2- thin the skin so the testes can dissipate heat quickly. It stands to reason that it may be easier to shave your jewel sac by using cooler shower water temperature... shrink them up and shave away. A cold shower and a close shave!
Remember the old style advertising
with small staggered road signs:
Careful with that axe, Eugene