This Refinery 29 article by Erika W. Smith talks balls and how to please them. Find an excerpt below and the full piece here:

“When giving a blowjob or a handjob, there’s one part of the anatomy that’s often overlooked: the balls. That’s right, it’s not all about the penis (though that’s certainly important, too). The testicles are packed with nerve endings, and they’re a major erogenous zone. Generally, they’re very sensitive — which means that many people prefer gentle touch. Though not everyone: just ask fans of cock and ball torture, aka CBT. "Before you engage in any kind of sexual activity, it's always about communication," sexologist Megan Stubbs, EdD, previously told Refinery29.”