"You have an RPG in your leg"

Editor's note: Watch Barbara Starr's report on Sanjay Gupta MD (Saturday at 430pET/Sunday at 730aET).

By Ashley Fantz, with reporting from Barbara Starr and Larry Shaughnessy

If it were a movie, the moment would play slowly.

The big, boyish eyes of 23-year-old Marine Cpl. Winder Perez would widen. His lips would part. The sound of chaos around him would be muted as he watched a rocket-propelled grenade zooming toward him.

Then, snapped back to real time, Perez would look down and think: "Oh, crap! I have an RPG in my leg!"

The whole thing, the entire, awful metal Nerf football-looking RPG was lodged inside his mangled leg. It was maybe a foot long. Its tail - fins, kind of - poked out.

In his shock, the Marine instinctively grabbed his radio to call for help, not realizing that it was totaled.

WATCH: How the RPG rescue unfolded

Perez didn't feel pain. He didn't feel anything. Adrenaline numbed him.

Another day in Musa Qala

It was mid-January in eastern Afghanistan. The Marine unit that Perez led had been deployed for four of their assigned seven months.

January 12 was like most days they'd seen in Musa Qala, the Fortress of Moses, in Helmand Province, a lawless and desolate stretch in southwestern Afghanistan where Pashtun tribes lived. It was hell there for American troops. Perez's men had taken fire several times. Musa was a Taliban stronghold.

Among many other dangerous jobs the Marines had, they were tasked with investigating when reports came in that an improvised explosive device had been found in the area. They got that kind of call on this day. So. They went to check it out, to verify that it was indeed the type of crude bomb that had killed thousands of Americans during the nearly 11-year war. Secure, verify, log, remove. That's what they did.

This call was no different. The IED they were called to check was legit.

When they finished their work, the Marines packed up and were headed back to the base.

It's unclear who fired the RPG that hit Perez. But it came from the south, a direction where the unit had caught fire before.

In the seconds after the Marines scrambled, they realized Perez was down. They ran to him and realized, in an awesomely frightening moment, they were looking down at an unexploded grenade.

Marines do what they have to do. It was no different in this case.

One of the troops leaned over Perez and joked, "I'm glad I have my protective glasses on."

A terrifying vote

The unit lifted and moved the wounded Marine quickly to a secure spot where they could avoid being hit by any more incoming fire. They tied a tourniquet and called for assistance.

A U.S. Army Medivac team that happened to be flying already was radioed.

Pilot Capt. Kevin Doo should head toward Perez's location.

He listened as he was told Perez's situation. The crew understood the stakes immediately.

Moving Perez into their helicopter meant moving the RPG. The device could explode at any minute. It could go off while they made the 65-mile flight to the nearest medical facility. All aboard could die. At the very least, medics working over Perez could take devastating shrapnel wounds if the RPG exploded.

"There was quite a bit of alarm among the crew at the time, as you can imagine," Doo said.

"Each of us on the aircraft had to agree to take this patient on," said Spc. Mark Edens, one of the medics aboard.

Each medic on the helicopter voted. It was unanimous. They were going to try to save the Marine's life.

'You have an RPG in your leg'

Perez would have likely bled out if the RPG had hit his femoral artery. The device was lodged only a few millimeters away.

When the medics touched down, troops lifted Perez and placed him in the helicopter.

Incredibly, he was still alert.

"Are we good?" Perez shouted.

The bird lifted off and flew to the nearest medical unit. Every minute felt like an hour.

They landed at a base, and Perez was gingerly removed.

By this time, he had started to feel. He asked Navy trauma nurse Lt. Cmdr. James Gennari for more painkillers.

Though the medicine was thick in his veins at this point, Perez was still clear-headed enough to notice that there didn't seem to be a rush of medics around his gurney.

"Where is everybody?" he asked.

"You have an RPG in your leg, and everybody's staying away from you," Gennari answered. He decided to tend to Perez alone thinking, "I am not going to ask somebody to do what I am not going to do."

Perez fully realized, "I'm not the one being protected. I am the one being protected from." He was quiet.

"I promise you," Gennari told Perez. "I will not leave you until that thing is out of your leg."

"Cool," Perez uttered, and then passed out.

An unusual recovery

With Perez knocked out, explosives expert Army Staff Sgt. Benjamin Summerfield came to help and began the crude but necessary work of getting that RPG out of his body.

Gennari grabbed the fins of the weapon protruding from Perez's flesh. The RPG budged a little.

An explosives expert stood next to Gennari and gingerly wrapped his fingers around the device. The RPG was stuck. The two then pulled the fins downward toward Perez's feet and yanked again.

Finally, the hulking metal came loose from Perez's flesh, and a specialist carried the device.

The medic stuffed the gaping hole in Perez's leg with sterile cotton and tightened his tourniquet.

He was carried into surgery.

Days later, Perez woke up in a military hospital in Germany.

He opened his eyes and saw nurses. He immediately reached down to check to see whether he still had his leg.

He felt for the leg that had been ravaged by the RPG. It was still there.

"Am I going to be able to keep it?" he asked.

Highly motivated

For months, doctors at Walter Reed National Military Medical Center, where he's been slowly recovering, have made sure that Perez has the best possible chance of not only keeping his leg but walking again.

In fact, Perez has recovered in a way that has shocked his doctors.

He's now walking with a cane. The braces he wore when doctors secured his shattered femur are now gone. Scars on his left leg are visible when he sits, and his black Nike shorts crop up a little.

"Imagine someone heating up a pole and putting it in your leg, and imagine that attached to that pole is a bomb," said Perez's trauma surgeon, Lt. Cmdr. Elliot Jessie. "We were concerned whether he would keep his leg or not. He had a big injury, a lot of soft tissue damage."

There's no simple explanation for why Perez has recovered so swiftly, he said.

It's lucky that the RPG missed his femoral artery, sure, said Jessie. But there's also something intangible about the way troops like Perez get better.

"He's a Marine, so he's highly motivated," said Jessie. "The first thing they want to know is when can I get back to my unit and when can I get back to being me. ... That makes taking care of them relatively easy."

Perez sat in a metal folding chair in a small room at Walter Reed, answering questions from a reporter. He looks like a typical 23-year-old. You have to look closely to see his scars.

He speaks clearly and calmly. He's polite and direct.

"I sure didn't want anyone losing their life over me," he said, recalling the trepidation the troops had to work on him.

He talks about why he enlisted at 18. No one in his family had been in the military, and it seemed like the right thing to do.

He grew up in the Bronx. He joked that being a Dominican-American requires that he love baseball.

'This is my job'

Some of his buddies from his unit are home now. They have visited him. Two weeks ago, he went with them to take in an Orioles versus Yankees game in Baltimore.

He's a Yankees fan, of course. "They lost but, hey, I got to see them," Perez jokes.

It was so nice to just be with them again, be normal, not the guy who went through all this hell.

"We went out," he said. "We drank a little. Did man stuff. ... We didn't really talk about stuff we went through over there."

Perez wants to be able to get on a patch of grass soon and hit a few balls.

Of course, he does. He will. When he says this, it isn't sentimental. His voice has an edge, but he's not going to lose control of his emotions, especially not in front of a news crew taping his interview for CNN.

"What, am I going to sit around and cry about it?" he says.

He sees a lot of guys in rough shape at Walter Reed. It's hard to compare bad experiences in war, but he's seen guys who've had it pretty awful.

There were guys in his unit who didn't come home, Perez is asked.

"We had our downs," he replies.

It's a hard thing to explain to people who haven't been there.

"From the time I got hit, to the time I got knocked out, I'll be honest with you, I wasn't thinking about it. It would've been a big explosion. I wouldn't have felt a thing," he said, stressing each word so that he can be better understood.

"The thing I was thinking about is: 'Who is going to lead my Marines? Who is going to take over for me? Are they better off without me?' " he said. "That's everybody's biggest fear - having to leave your Marines behind.

"This is my job. My job included a lot of stuff that may happen. One of those things happened to me. But those guys, those guys, they were there for me."

Barbara Starr and Larry Shaughnessy contributed to this report.

Watch Gennari and Summerfield try to remove the RPG: