Chimpanzees have been seen showing some very clever behaviour - they've apparently been using spears to hunt other animals.
Researchers saw chimps in Senegal make spears from branches, and then jab them in hollow trees to get at anything that might be hiding inside.
We've known chimps use things like stones as tools for a while, but this is the most advanced tool seen yet.
This discovery is making people look at chimp society in a new way.
A spear made by the chimps
Interestingly, it is only the female chimps that hunt with spears.
It's thought because they can't rely on strength like the males, the females have had to come up with new ways of getting food.
Jill Pruetz, one of the researchers, said the chimps were at a stage that our ancestors were thought to be at some six million years ago.