Adam has a phobia of tarantulas, so naturally Caveman Rob picks two of the world’s nastiest ones for them to endure, including a tarantula with the well-deserved nickname: “Orange Bitey Thing”.

Adam and Caveman Rob get bitten by one lizard whose venom is in doubt–but not its ability to latch on and tear flesh–and another whose venom is notoriously painful. The shocking results set new records for the Pain Index.

Adam and Caveman Rob wrap up the season in Indonesia, with the two worst bites to date, from a Giant Asian Centipede and a 16-foot Reticulated Python. Vomiting, stitches and rivers of blood make them ask if they are able to continue their research.

Rob and Adam test the pain dished out by a trio of unlikely creatures commonly kept in home aquariums–and they proceed to ruin the image of a popular cartoon movie character for millions of children.

In a tribute to the godfather of the Pain Index, Dr. Justin Schmidt, Adam and Rob tangle with a new batch of extremely painful–and deadly–insects. And one colony of ants kicks the Schmidt out of them.

It's America vs Australia in a battle royale of pain administered by sharks. After getting stung by both, Adam and Rob realize that when their countries win, they lose.

The guys encounter two legendary creatures of the Amazon: the Bullet Ant and the Piranha. After hours of pain from the Bullet Ant, Caveman Rob dips his blood covered arm in a tank of Piranhas. What follows is a bloody and painful mess.

A wildlife biologist and professional animal handler get bitten and stung by some of the most dangerous animals and vicious stinging insects in the world in an attempt to create a complete and comprehensive pain index that will ultimately help save lives.

The crew finds out that the swamp may be manmade.

An underwater hunt for the possibly deadly scorpionfish in the Baja, ocean leads to a toxic sting that puts Adam in danger and matches the highest pain score to date, while the Toe biter results in the weirdest pain profile yet.