Even the "Kings of Pain" have a limit when it comes to voluntarily being bitten by poisonous animals ... telling us rattlesnakes are a no-go.
History Channel stars Adam Thorn and Rob Alleva joined us on "TMZ Live" Thursday and told us why they're down to keep getting bitten by animals whose poisonous venom is geared towards defensive purposes, and where the cutoff lies.
The guys puked and were hospitalized following a bite from a Mexican beaded lizard, and they say that's about as much as they can handle ... because if they were to cross into deadly venom territory, the stakes are obviously much higher.
The way Adam and Rob see it -- rattlesnakes, for example, are on the attack when they take a poisonous bite -- and those bites can have potentially life-changing consequences, or even result in death.
In the second season of their show, they're bitten by lizards, urchins, piranhas, lionfish, centipedes and this scary beast ... the tarantula hawk wasp.
Adam and Rob are all about pushing their boundaries ... but some animals are clearly out of bounds.
The "Kings of Pain" aren't just doing this for bragging rights either ... they've also got scientific reasons behind their death pain wish.