chimpanzees or orangutans in captivity sometimes tried to lure human strangers over to their enclosure by holding out a piece of straw while putting on their friendliest face.
“People think, Oh, he likes me, and they approach,” Dr. de Waal said. “And before you know it, the ape has grabbed their ankle and is closing in for the bite. It’s a very dangerous situation.”

After dolphin trainers at the Institute for Marine Mammals Studies in Mississippi had taught the dolphins to clean the pools of trash by rewarding the mammals with a fish for every haul they brought in, one female dolphin figured out how to hide trash under a rock at the bottom of the pool and bring it up to the trainers one small piece at a time.