In Heart of Darkness, what did the wilderness whisper to Kurtz?
Thinking about Kurtz and how he has survived and thrived in the jungle, even while slowly dying from its influence, Marlow comes to realize that Kurtz, like all men, was imperfect, but that he had refused to recognize it.
...there was something wanting in him—some small matter which, when the pressing need arose, could not be found under his magnificent eloquence. Whether he knew of this deficiency himself I can't say. I think the knowledge came to him at last—only at the very last. But the wilderness had found him out early...
(Conrad, Heart of Darkness, eNotes eText)
He goes on to wonder if the act of living in the jungle has allowed Kurtz to see, for the first time, his own mortality and the atrocity of his acts. It is possible that Kurtz, on recognizing his flaws and his limitations, instead embraced violent acts as a way of coping, since he couldn't fix himself any other way. In a sense, after the jungle "whispered" to Kurtz that it understood him, Kurtz was forced to lash out against it and its inhabitants to avoid being consumed by the jungle itself.