The Devil's grimmace.

An interesting fragment by Gisela Telis in ScienceNow:

When 15th-century Europeans first landed on the Bahamas, Cuba, and Hispaniola, they met with the "devil's grimace." That's what these foreigners dubbed the faces with bared teeth that adorned everything from necklaces to ceremonial bowls created by the native Taíno people. European chroniclers interpreted the motif as a ferocious animal's snarl or a skull's grimace, signs of the heathen islanders' aggression. But they were wrong, researchers report in the latest issue of Current Anthropology. By studying teeth-baring in humans, chimps, and rhesus macaques and comparing these to the Taíno depictions, scientists determined that open-lipped, closed-jaw displays show submission, benign intent, and even happiness—but not aggression. So the "fiendish" faces that so troubled Europeans were most likely just smiling, to signal—ironically enough—social cohesion and connection.