I often and frequently use my own voice for sound design (and music) in many different aspects, not just human or animal interactions, but for example I was working on one short film that was on the virge of art-film/short film. No real story just an emotion. And I got down to business, started foley recording and in one scene the main character opens a cabinet. I just couldn't get that cabinet door to sound right. I wanted it to have a creak and something "outer-worldly", so what I ended up doing was recording me just imitating the door and combining it with the real creak, and it just worked totally right.
Soooo... What about making a film with sound design entirely created with voices? Has anyone seen anything like that? Is it possible? Would it be fun?