I have just realized that while locked and becoming arroused my sack tightens and even slightly expands. Whats going on? Is extra blood going to my balls/sack in a similar way as my my penis? I tried Google but only got porn and stupid stuff listed. It doesn't hurt at all just has me curious.
No, I'm sitting still the whole time and the sack is loose and not stretched until something gets the cock excited then the sack bulges a bit and tightens up.
Mechanically speaking, it is a natural occurrence during excitement. It is a natural protection of your boys, when in action, you don't want them swinging free. All sorts of bad things can happen when moving violently, and in a defenseless position. Our bodies tighten it up a bit. It's normal, as far as swelling? Well, they tend to swell when caged and not allowed to tighten fully.
That is normal. Happens to me all the time. Sometimes I have to make myself cool off because it gets very tight and the ring digs into me.
Have you ever just sat very still and watched? The scrotum is never completely static, especially if there is a touch of warm/cool air… it contracts and expands and flows like oil on water, constantly adjusting to maintain a consistent temperature.