Wild chimpanzees in Uganda have been caught on tape developing a new drinking utensil: a mixture of moss and folded leaves that they place in their mouths and then dip into water.

Although it has long been understood that chimpanzees learn by observing one another, scientists say this is the first time humans have witnessed the origins of such behavior. A new study in the journal PLOS Biology describes the phenomenon and how the researchers watched it spreading from chimp to chimp.

Previously, the chimps used only leaves to make the tool. It is not clear whether the new mixture is an improvement, but an author of the study, Thibaud Gruber, a primatologist at the University of Neuchâtel in Switzerland, said, “One day the alpha male decided to add some moss, and from that moment it took off.”

The dominant female in the group watched the alpha male, and then tried making the same tool for herself.