"When you first started this, did you sit down at your desk and look at your hand? And figure out how it worked?" Pelley asked.
"Well, most good engineering is some adaptation of what nature does," Kamen replied.
It all began by creating dozens of gears, joints and computers that mimic nature's design. But then came the hard part: meeting DARPA's demand for an arm no larger than the average human's and no heavier than nine pounds.
Kamen showed Pelley a part of the DEKA arm which contained three processors. "Think of this as three PCs worth of computing power. And all of this just fits, it's round because it just fits in the wrist joint."
Asked what the toughest part of the engineering process was, Kamen replied, laughing, "All of it."
The prototype had 25 circuit boards and 10 motors. But it would be no good at all unless the patients were willing to accept it.
"We went and started talking to the real patients, the potential users, down at places like Walter Reed. And immediately, we were shocked to learn, even just the hollow plastic shell that they wear when they're out and about, it sweats, and it hurts, and it irritates. And we came back and realized that if we build the world's best nine-pound arm, but nobody will wear it because 24 hours a day, or 12 hours a day, of wearing a nine-pound arm is going to be irritating, and frustrating, we said, 'We've got a way bigger problem here,'" Kamen remembered.
So Kamen's team created a new way to connect the DEKA arm to the body using tiny, round balloons.
"And you'll notice now, if I hit this button, these things are inflating. And that's a nice, gentle pressure there. But if that's displaced all over your whole shoulder, that's an enormous amount of structure," Kamen said, demonstrating how the balloons work.
"So, now the arm is gripping tight on the whole shoulder…so you can lift something heavy," Pelley observed, watching the arm in action.
"Right. And as soon as he's not gripping tight and heavy, one or the other might just deflate," Kamen explained.
Kamen asked Fred Downs, the VA official in charge of prosthetics, to take off the hook he'd been wearing for 40 years and give the new arm a try.
The arm Downs tried out is controlled by flexing the shoulder and pressing buttons built into his shoes - almost as if he's typing with his toes.
Downs told Pelley he was very skeptical. "Because I've seen lots of inventions come along in my years of being in charge of prosthetics, and so some great stuff, but in the long run it doesn't really work because your body only has so much tolerance for gadgetry."