Prehistoric talk is a bad idea. Unless you want it to have a B movie feel, but I personally wouldn't like it.
I was thinking maybe give the cannibals a unit that uses javelins that have been set alight, kind of like a Fire Shaman type troop. I've been REALLY enjoying it, though. Fighting on foot is awesome, I do not miss horses at all.
Are thrown rocks and skulls supposed to be more accurate (and deadly) than thrown axes and javelins?