Three years ago, a stone-throwing chimpanzee named Santino jolted the research community by providing some of the strongest evidence yet that nonhumans could plan ahead. Santino, a resident of the Furuvik Zoo in Gävle, Sweden, calmly gathered stones in the mornings and put them into neat piles, apparently saving them to hurl at visitors when the zoo opened as part of angry and aggressive \"dominance displays.\" But some researchers were skeptical that Santino really was planning for a future emotional outburst. Perhaps he was just repeating previously learned responses to the zoo visitors, via a cognitively simpler process called associative learning. And it is normal behavior for dominant male chimps to throw things at visitors, such as sticks, branches, rocks, and even feces. Now Santino is back in the scientific literature, the subject of new claims that he has begun to conceal the stones so he can get a closer aim at his targets—further evidence that he is thinking ahead like humans do. The debate over Santino is part of a larger controversy over whether some humanlike animal behaviors might have simpler explanations. For example, Sara Shettleworth, a psychologist at the University of Toronto in Canada, argued in a widely cited 2010 article entitled, \"Clever animals and killjoy explanations in comparative psychology,\" that the zookeepers and researchers who observed Santino\'s stone-throwing over the course of a decade had not seen him gathering the stones, and thus could not know why he originally starting doing so. Santino, Shettleworth and some others argued, might have had some other reasons for caching the stones, and the stone throwing might have been an afterthought. In the new study, published online today in PLoS ONE, primatologist Mathias Osvath of Lund University in Sweden—author of the earlier Santino paper—teams up with Lund University primatologist Elin Karvonen to report new observations of Santino\'s behavior during 2010. Santino\'s first attempts to throw stones during 2010 came during the May preseason. As a zoo guide led visitors toward Santino\'s island compound, the chimpanzee began to engage in a typical dominance display: screeching, standing on two feet, and carrying a stone in his hand. The guide and the visitors retreated before Santino began hurling the stones, and then advanced again for a total of three approaches. When the people returned about 3 hours later, Santino advanced toward them, holding two stones, but he did not act aggressively, even picking up an apple from the water surrounding the island and nonchalantly munching on it. But when Santino got within close range, he suddenly threw one of the stones. (It didn\'t hit anyone.)