The only true way to gurantee a quick kill are to stop the the transmission of information from the brain the muscles, ie head , neck shots. Or to insure very quick loss of blood pressure, ie heart lung/major arteries. Shooting in the gut will kill, indeed. But it tends to be slower blood loss or shock, which takes a little longer than a shot to the vitals.
Interesting that he was eating grapes by the way........... Hardly the diet of a hunter, is there a lack of prey around?