Brave Aron Ralston was hiking in the state of Utah when a boulder he was holding on to slipped and rolled onto his arm.

For five days he was trapped, and when his water ran out, Aron decided he had to do something to get free.

But since he couldn't move the boulder, his only option was to use his penknife and cut off the part of him that was trapped - his right arm, just below his elbow.

And that wasn't all he had to do to get to safety.

Once he's applied some first aid Aron had to abseil down from a 21-metre high ledge and start hiking back towards his vehicle.