Over the many many years of intercourse sex and blow jobs. Few rarely interacted with my balls. Maybe some feeling me up in my pants, etc.
My wife, is the only one who likes to watch the balls move - by themselves. *I* never knew they moved until she pointed it out to me. She used her phone to make a video so I could see.
So yes, when your man is laying down relaxed (naked). put the penis up (not resting on the balls) and watch them move on their own.
On top of that, she loves to play with my balls - even sometimes when I am asleep. She'll hold them, massage them... suck on them.
PS: one of the many reasons why I love her.