A nocturnal rat that resembles a porcupine coats it quills with a plant toxin, a new study says. African hunters use the same substance in order to make elephant-grade poison arrows.

No other animals use a truly deadly external poison, researchers said.

Scientists suspected that the rat might be using poison because dogs often grew ill or died after they encountered the rodent and because it has a black-and-white warning coloration.   

The researchers made their discovery after they saw a crested rat with branches and roots of the Acokanthera tree. The tree's bark holds the toxin ouabain.  

The rat chewed through the tree's bark but avoided the nontoxic leaves and fruit, then applied the drool to its hair. 

According to study co-author Tim O'Brien, a biologist with the Wildlife Conservation Society, the rodent is similarly aggressive in other ways, and it has very tough skin and a reinforced skull. 

Ouabain causes paralysis at small doses and heart attacks and high doses.   

O'Brien also told National Geographic that "the dogs that we know of that have attacked the crested rat have suffered everything from temporary paralysis for a couple of weeks to death."

It remains unclear how a young rat discovers this intrinsic tendency.