A male chimpanzee in a Swedish zoo planned hundreds of stone-throwing attacks on zoo visitors, according to researchers. Keepers at Furuvik Zoo found that the chimp collected and stored stones that he would later use as missiles. Further, the chimp learned to recognise how and when parts of his concrete enclosure could be pulled apart to fashion further projectiles. The findings are reported in the journal Current Biology. There has been scant evidence in previous research that animals can plan for future events.