Fernando Costa

The physical strain on survivalists is already enormous -- and then a huge storm tests the resistance of the participants and their shelters.

Each pair meets to walk in search of water and a place to spend the first night, protected from predators and the cold of the Argentine Chaco.

The survivalists evaluate possible strategies to reach the extraction point and two of them have a strong discussion; faced with a lack of protein, one participant executes the riskiest plan of the challenge: hunting an alligator.

Survivalists are surprised by alligators and piranhas infesting Chaco's rivers and fearful of large cats prowling their camps at night.

One survivalist scores the biggest hunt of the challenge. Chaco's coldest night yet leaves participants on the verge of hypothermia.

The storm's aftermath brings difficult consequences to the camps, including damp firewood, swarming insects and growing rivers filled with alligators.