Nat-balls

When one has their testicles so far into their abdomen, they can't feel where they are. My feeling their genital region. The term refers to the Nantahala river, and refers to the extreme temperatures of the river that Are known to cause the testicles of kayaker to retreat into the abdomen.

Person 1: Bro I got Nat-balls

Person 2: did you shred the Nantahala?

Person 1: Nah dude, just nervous AF for my exam...