If you’ve seen the movie 127 Hours, you know how Aron Ralston’s story goes. But for those who haven’t, it’s a bit of a shocker.

In 2003, Ralston was hiking alone in Bluejohn Canyon in Canyonlands National Park in southeast Utah. While he was descending into one of the remote and exceedingly narrow canyons, a boulder fell and trapped his right arm. For five days he survived off of packed water and snacks, hoping someone would find him. Trouble was, not only was the spot remote, but he also hadn’t told anyone where he was going.

Realizing he may never be found (and running out of supplies) he was forced to amputate his arm by cutting through the bone using his multi-tool that included a knife. After freeing himself, he began the seven-mile walk back to his truck. During his journey, a family discovered him and alerted authorities.

He lost 40 pounds during his ordeal, and somehow, miraculously, avoided bleeding to death. He now continues to mountaineer and works as a motivational speaker.

Douglas Mawson—cannibal or hero? Mawson was an Australian geologist and explorer who infamously explored the frozen continent with a team of fellow adventurers in 1912. In December of that year, Mawson and two other expedition members left the main base at Commonwealth Bay, embarking on a 300-mile exploration into the interior of the continent to gather scientific data and specimens. Tragedy followed.

One of the men, a young British soldier named Belgrave Ninnis, plummeted down a crevasse on a sledge, along with several of their best dogs and many of the team's supplies. For several weeks, the two others, beset by scurvy and other ills, struggled to return to camp, subsisting first on the remaining dogs, then on starvation rations. Ultimately, Xavier Mertz, a Swiss mountaineer and skiing champion, died from exhaustion, starvation and possible toxicity from eating dogs’ livers.

Determined to return with the research data, Mawson battled the elements for 30-some days, finally stumbling into base camp in February of 1913, emaciated, frost-bitten and exhausted—only to discover he had missed the ship retrieving the rest of the crew by hours. While deemed a survivor hero (he was later knighted and his face now adorns the Australian $100 bill), there are questions about what extreme measures he may have taken to stay alive. A 2013 biography of Mawson suggests he may have purposefully set his and Mertz's starvation rations at a level that would have hastened his companion's death, and that he boiled and ate Mertz’s corpse in order to survive. Mawson's descendants decry the allegation.

Mauro Prosperi is an Italian police officer who gained worldwide fame after getting lost in the Sahara Desert in 1994. A keen athlete and long-distance runner, Mauro took part in the 1994 Marathon of the Sands in Morocco, a six-day-long endurance race in one of the driest and barren environments on the planet.

During the race, a sandstorm caused Prosperi, then 39 years old, married and father to three children, to become disoriented and lose his way. One day after going off track, he found himself in an abandoned Muslim shrine in Algeria. In order to survive, he killed and ate bats. For fluid, he was forced to drink his own urine, lick dew off of rocks and suck moisture out of his wet wipes.

Assuming he would never be found, he slit his wrists with a pen knife from his supplies. However, it was such a dry heat that the wounds clotted and he was forced to go back into the desert and attempt to find help.

For nine days he walked through the desert and ate insects and reptiles. Finally, he found a small village. From there he was flown to a hospital, where doctors said his liver had almost completely failed.

Having traveled 180 miles in all, Prosperi lost 35 pounds in body weight during his ordeal in the desert; it took several months before he could eat solid food again. But he has remained an enthusiastic runner and even returned and completed the race in 2012.

José Salvador Alvarenga is a Salvadoran fisherman who spent 13 months adrift at sea. He is the first person in recorded history to have survived in a small boat at sea for more than a year.

On November 17, 2012, Alvarenga set off on a professional fishing trip with a young fisherman named Ezequiel Cordoba, with whom he had never worked. Having embarked from a fishing village on the Pacific coast of Mexico's southern Chiapas state, they planned to be out for about 30 hours hunting shark, tuna and mahi mahi. A few hours into their voyage, a storm struck that lasted five days and blew them off course. Alvarenga called his boss on the ship’s radio for help, but it—and much of the rest of the boat’s electronics—had been disabled by the storm. The boat's motor was also damaged.

A search party was sent, but after two days with no success, their boss gave up and assumed they had drowned.

Alone and without food or supplies, the two fishermen survived by eating raw fish, turtles and jellyfish. They drank rainwater and turtle blood. As weeks turned to months, Cordoba became severely unwell from eating months of raw food and died.

Alvarenga then endured another nine months alone at sea, until he eventually spotted a small island. Abandoning his boat and swimming to shore, he almost immediately met a local couple who alerted authorities. He had reached the Marshall Islands.

His journey lasted 438 days and his voyage is estimated to have covered between 5,500 to 6,700 miles.

On January 23, 2006, Ricky Megee was driving through the Australian Outback on his way to a new job when he picked up a group of hitchhikers. The next thing he remembers is waking up in a shallow grave in the Outback wilderness with dingoes scratching at the plastic wrapped over him.

Unable to locate his car and clueless about his exact whereabouts, Megee was forced to survive for 71 days out in the rugged, perilous terrain.

He constructed a “humpy” (a basic form of shelter) using branches and leaves and says he mainly lived off eating frogs, leeches, snakes and drinking his own urine. At night, he barricaded his shelter with rocks, to prevent dingoes from trying to eat him as he slept.

Eventually, workers on a remote cattle ranch stumbled upon Megee, who had become skeletally thin, having lost more than 100 lbs. He was taken to a local hospital and treated for severe dehydration and malnutrition.

What exactly had happened to him remains a mystery. Authorities originally expressed skepticism about his story. (He claimed the hitchhikers likely drugged him.) His vehicle was never found.