"Chimpanzees in Senegal have been observed making and using wooden spears to hunt other primates, according to a study in the journal Current Biology."
By strange coincidence, the new issue of Science News has an article about evidence showing that chimps were using stone tools to crack nuts at least 4300 years ago. Cracking nuts with a rock is a far cry from sharpening a spear, though.
+1 for the thumb alone
It's not really clear from the article whether this is something the chimps have been doing all along and we are just now discovering, or we have been watching them all along and they just started doing this. Either way, other animals using tools makes me uncomfortable.