In this photo provided by the San Diego Zoo, two lowland gorillas forage for raisins in the grass of their exhibit at the San Diego Zoo on Tuesday, March 26, 2013, in San Diego. Paul Donn and Ndjia were treated to the fruit as part of the Zoo’s Play Days event, which highlights the various ways the zoo provides enrichment activities for the animals to encourage and reinforce natural behaviors including hunting, exploring, climbing and swimming. (AP Photo/San Diego Zoon, Ken Bohn)