I observed this type of training “backstage” in the off-exhibit areas at the Oklahoma City Zoo and Botanical Garden, where gorillas like Gracie and her silverback father, Tatu, were being taught to paint by primate keeper Jennifer Davis. First, a gorilla is offered a brush and taught (or enticed), through praise and the reward of a tasty morsel, to give it back to the keeper, passing it through the wire mesh that separates them. This is more difficult than it sounds, because sometimes the gorilla wants to keep the brush to chew on.

Next, she is taught to touch the brush to a piece of paper held by the keeper on the other side of the mesh — this is called “targeting,” and it was the step Gracie was on after two months of training, when I observed. Each successful touch evokes praise, encouraging the gorilla to repeat it. Eventually the brush is loaded with nontoxic paint, so that as the gorilla passes it back to the keeper, the paint hits the paper and makes a mark. As the marks accumulate, a “painting” emerges.

But while the products get called gorilla paintings, they’re really a cross-species collaboration. Usually the caretaker selects the colors, manipulates the paper so that the brushstrokes fill the page instead of smearing into muddiness, and decides when the piece is done. Occasionally, the publicity department even gets into the act, deciding what color schemes will sell best. Occasionally, the animal selects the colors, as does Toba the Orangutan at the Oklahoma City Zoo, and sometimes the animal refuses — despite entreaties — to add another stroke, as Congo reportedly did. Yet despite this control, paintings by animals are always an ironic reminder of their captivity, because no animal paints in the wild.