BBC NEWS | Science & Environment | Zoo chimp 'planned' stone attacks
http://news.bbc.co.uk/2/hi/science/nature/7928996.stm

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.

This is fascinating. Experts say this shows that the chimp was "anticipating a future mental state - an ability that has been difficult to definitively prove in animals."

Chimps behaviour shows they are more intelligent than it seems