Zookeepers noticed, after observing Santino behind blind glass, that the chimp had been busy stockpiling ammunition in anticipation of the visitors, dragging stones from a protective moat and even thumping chunks of concrete into rough discs. He made the piles of stones only on the part of his island facing the crowds and his behaviour shows that forward planning isn't a uniquely human trait.
To control his behavior, and keep his hormone levels down, zookeepers castrated Santino. Since then, Santino has been observed to be more playful and is growing a "Buddha belly".
On the 19th of March 2009, Santino and his attacks were mentioned as a part of "when animals attack our morals", on The Colbert Report, which brought to light the poor understanding that exists between man and his ancestral cousin. Also discussed was how these incidents are not limited to "animals" alone, but humans in general.
- "Zoo chimp 'planned' stone attacks". BBC News website, 9 March 2009.
- Current Biology, volume 19, issue 5, 10 March 2009, pages 190-191.
- "Chimp who threw stones at zoo visitors showed human trait, says scientist". Guardian News website, 18 March 2009.
- May 2009 Scientific American Magazine