Do women comment on guy's nuts amongst themselves?

Pretty much the only people that care about balls are those that are attached to them.

...never forget 'em

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Now can we talk about the scrotum?

Do guys talk about womens labias among themselves?

Constantly.

There are a decided lack of sex moves involving balls.

True. All that comes to mind is the Two Dogs in a Bathtub.

I ended up talking about balls at a bar last night. As the owner of the only pair at the table, I had to explain some of the various elastic features of the testes.

Indeed. I've been wracking my brain for synonyms for that one and coming up blank.

BraveArt and I did come up with Panning For Gold (that doesn't sound good written out, does it?), which is the jostling of the jewels during oral sex. The accompanying hand gesture really sells it.