For example, whereas poisonous insects tend to advertise their unpalatability in bright colors like red, orange and yellow — the better to warn off their major predators, the diurnal, keen-eyed birds — most mammals and their mammalian predators are nocturnal or crepuscular, dawn and duskular. Color is wasted on them, but strong contrast between dark and light is not.

This is why skunks, zorilles (also known as polecats) and the African crested rat have independently converged on a similar pelage theme of black against white. The pattern is unmistakable in very low light, and its message is too: You’ve seen me. I’m noxious. Now buzz off.

In their fetchingly titled paper, “A Poisonous Surprise Under the Coat of the African Crested Rat,” Jonathan Kingdon and Fritz Vollrath of Oxford University and their colleagues described the complex of traits that give rise to the rodent’s rottenness.

The researchers determined that the rat spends many hours gnawing on the bark and roots of the Acokanthera tree, from which it extracts the same curare-type heart toxin that African hunters have traditionally used to kill elephants. The rat then slavers the toxic masticant onto tracts of specialized hairs running along its flank.

Those hairs, when observed under a scanning electron microscope, look very different from ordinary fur, Dr. Vollrath said. Each outer shaft is stiff and full of holes — like a dead cactus, he said — and inside are a series of long, fluffy microfibers. The researchers showed that the applied toxin seeps through the outer holes of the hairs and is wicked up and stored by the fibers, lending the rat twinned flank strips of doom.

One little nip is all it would take to sicken or even kill a predator, and the crested rat is well equipped to endure exploratory bites, Dr. Vollrath said: Its hide is unusually thick, and its head is helmeted like a turtle’s. Whether through trial and error or by following an enlightened elder’s example, Africa’s many carnivores give the rat a wide berth.