Tarzan let him up, and in a few minutes all were back at their vocations, as though naught had occurred to mar the tranquility of their primeval forest haunts.
But deep in the minds of the apes was rooted the conviction that Tarzan was a mighty fighter and a strange creature. Strange because he had had it in his power to kill his enemy, but had allowed him to live — unharmed.

Ch. 12 : Man's Reason - Tarzan of the Apes (1912)