Baker, K. C. 1997. Straw and forage material ameliorate abnormal behaviors in adult chimpanzees. Zoo Biology 16, 225-236.

In an [successful] effort to reduce abnormal behaviors, especially regurgitation and reingestion, and promote higher activity levels [locomoting and playing], straw and scattered forage material were added to the enclosures of 13 indoor-housed chimpanzees living in pairs and trios.