From what I understand, the penis is supposed to have a mobile skin system, so it can glide up and down. The “death grip” is when guys get a tight grip and crank it up and down to get maximum stimulation. Circumcision can (often?) remove the entire mobile skin system, leaving the penis skin as tight as the skin on, say, your thumb.

Get a tight grip on that, and start cranking, and it’s basically trying to rip your dick off.