Several species of skinks on the island of New Guinea exhibit a curious characteristic: They have bright-green blood. The coloring comes from high levels of biliverdin, a toxic pigment produced by the breakdown of old red blood cells. It should kill the skinks—but it doesn’t.

Humans also produce biliverdin, which then changes into another toxic pigment, called bilirubin. The liver filters this toxin from our blood. But if this organ isn’t functioning properly, bilirubin builds up. The result is a condition called jaundice, which turns a person’s eyes and skin yellow.

Scientists are studying how skinks resist biliverdin’s toxic effects. “This research could help doctors treat people with dangerously high levels of bilirubin in their blood,” says Christopher Austin, a herpetologist at Louisiana State University who studies the lizards.