There's an abundance of scientific evidence that elephants are whip-smart, feeling creatures, who form complex social networks and who can feel distress (and perhaps even empathy). And researchers recently found that wild elephants are using their intelligence to recognize dangerous humans based on a very specific set of characteristics: gender, smell, clothing and even the langauge they speak.

In Kenya, Maasai men occasionally hunt elephants in retaliation for wounding or killing humans or for raiding crops. Elephants have caught on to this fact. Previous studies, National Geographic reports, have shown that elephants recognize and respond to the Maasai by their bright red robes, while they tend to ignore the brown-clothed Kamba, another ethnic group in the region. If they see a red cloth, the elephants tend to become angry; if they catch the scenet of a Maasai man, they flee the scene.

Most recently, researchers played recordings of various people talking—Maasai men, women and younger boys, and Kamba men—to see how elephants who heard those voices would react. The phrases the people used weren't aggressive, just things like, "Look, an elephant!" NatGeo:

Over a two-year period, they carried out 142 such playbacks with 47 elephant families, each time playing a different human voice through a concealed speaker placed 50 meters (164 feet) from the animals. They video-recorded the elephants' reactions to the various human voices, including a Maasai man's voice they altered to sound like a woman's.

The elephants' ears are fine-tuned for danger, it turns out. When the Maasai man—and only the Maasai man—spoke, the animals would silently retreat, NatGeo reports. They got a bit defensive when they heard the Kamba man speak, but their reaction was not nearly as extreme as the one elicited by the Maasai man.

As NatGeo points out, unfortunately for elephants, they probably have not had enough time to learn that such a response would also serve them well for avoiding encounters with ivory poachers, who are oftentimes foreigners to the area.