Reinhardt, V. 1992. Foraging for commercial chow. Laboratory Primate Newsletter 31(2), 10.

While sitting on swings, platforms or other elevated structures, or clinging to the mesh, individual animals seize a piece of chow [fruit, vegetable or bread] and retrieve a piece [through the mesh of the ceiling]. This simple 'food puzzle' not only promotes non-injurious foraging skills but also keeps the floor relatively clean by avoiding undue spoilage of food. The animals only work for food that they actually eat.