The interesting thing about nut cracking is that chimpanzees basically need
three objects to come together.
They need a hammer, they need the nuts, and they need the anvil.
And that makes it already a kind of a very sophisticated type of tool use.
For some nuts, a wooden hammer will not do it because the nuts are sometimes very hard.
You need a stone.
And so you need to transport the stone--that is quite rare in the Thai Forest--
over a long distance to bring it to the tree where the nuts are being produced.
We have followed the transport of this hammer in the forest.
We marked all the stones, and we looked at their locations,
and we followed how the chimpanzee transported them.
And we found out that the chimpanzees have a very precise mental map of the forest.
They know where the stones are.
And they were able to plan and to compare the distances of the stones to a target tree
where there was no stone and to select--from all the stone in the forest--
the one that was closest to the target tree within a given class of weight.
So quite an elaborate mental calculation is going on in the head of a chimpanzee
when he just wants to have a hammer to crack a nut.