How its called this?

XTube Videos
How its called what he does with his balls (near the end) when they somehow "go tight" his dick (its not the proper explanation, check vid..)?
And how it's possible to do that?

Thanks

Every guys balls will raise up close to his body when he's about to cum.

For some guys, their balls raise up and their sack becomes tight and sits right under their cock, but for some guys, their balls are pulled up past that point and sit either sit of their cock.

It's kinda common.

He's got nice balls though.

Mine don't do this, I've always wondered if it's painful for those that do.

nah, doesn't hurt a bit

mine do that, and it doesn't hurt. unless someone smacks them or something, then i'd probably pass out.

Very rarely, if I'm seriously "beating" my meat, the force will put my balls back in the socket they dropped out of. They can be popped back out too, fortunately.

my balls get close to my cock too, but not like that video, the ballsac gets tight., but other times they hang and chill..

who wouldn't want to be close to the cock it's just instinct i guess..

Yeah, well its normal that they get close to cock... but like that vid it's wicked... and so in my little mind I thought that somehow he was doing that on purpouse :)

Not sure what the official tightening of the balls is called....although the video made me seasick.....what a gorgeous pair of duck egg shaped nuts that guys has.....the term I would use is HOT, HOT, HOT!

Sometimes they do get a little tight when i'm close to cumming, like if i've been edging for awhile. When this happens, I usually use the other hand to massage and tug on 'em.