When a male rubs his hand along his scrotum, and then proceeds smells his hand--now scented with his ball musk--, he has just performed a Sack Sniff. Often performed, but rarely acknowledged in polite society, the Sack Sniff is an interesting cultural sensation that begs for an evolutionary-psychological explanation. The male executing the Sack Sniff will often report enjoying the scent, or at least conceding that he finds himself executing the Sack Sniff frequently. Perhaps he is checking levels of pheromones in his system as a form of virility/fertility auto-monitoring behavior.
Male 1: Did you really just wipe your balls with your hand and then smell it?
Male 2: Obviously. You never sneak a Sack Sniff?
Male 1: (sheepishly) Yah, I guess I do...
The man enjoyed a refreshing Sack Sniff while undressing to shower.