Apparently Gorillas have been known to use tools for food gathering but this is the first time in 40 years they have witnessed another tool application, gauging the depth of water for safety... Very Cool Article
From the Article...
"Most great-ape tool use is based around the retrieval of food," says
Gillian Sebestyen-Forrester, who studies gorilla communication at the
University of Sussex, UK. "But the gorillas have understood that they
can extend their sensory experience and find out more about their
environment by physically extending their bodies with an inanimate
object. This suggests that the gorilla is capable of some mental
calculation and abstract thought."