You cannot poison an opossum

As we established last week, marsupial biology is freaking crazy.Here's more proof. For this, you don't even need to go to exotic Australia. The common American opossum produces a protein called Lethal Toxin-Neutralizing Factor (LTNF). This protein does pretty much what the name implies—seeking out potentially deadly poisons and neutralizing them. The benefit: Opossums are all-but immune to the venom of poisonous snakes. (Including the venom of snakes native to continents where the common American opossum does not live.) But it gets weirder, as Jason Bittel explains on the BittelMeThis blog:

So they took some rats and injected them with LTNF, then pumped them full of otherwise lethal doses of venom from Thailand cobras, Australian taipans, Brazilian rattlesnakes, scorpions and honeybees. But the rats just laughed in their faces.
“Dude,” said one scientist, “we have to kill these rats. Do you watch AMC’s Breaking Bad?” The other scientists nodded of course because everybody watches Breaking Bad. So next they tried to kill the rats with ricin, an extremely lethal poison made from castor beans. (How lethal? Just ask Georgi Markov, the real-life Bulgarian defector killed by a ricin umbrella gun. That’s right, I said ricin umbrella gun.)
Alas, the ricin was a no-go. The now-snooty rats danced Ring Around the Rosie.
“That’s it!” screeched the lead scientist. “It’s time to release the botulinum toxin. Surely this will conquer the awkward opossum’s super serum!” But after many maniacal laughs and a few bolts of lightning, the rats were still alive.
(The paper does not mention what became of the super rats. I can only assume they went on to write “The Secret of Nimh” while the evil scientists lost their rat-killing grant.)

Read the research paper
Read the rest of Jason Bittel's story on the strange and wonderful biology of opossums