A healthy bull calf born on a ranch in southeast Brazil astonished scientists who were expecting a female cloned from an adult cow.

Although not Brazil’s first cloned calf, it may be the first cloned from somatic, or adult, cells. And scientists have yet to explain how they got a bull from ear cells of a cow.

The project’s chief veterinarian, Jose Visintin, said on Monday the experiment “either erred in the laboratory or in the field.”