"I've got to kill the damned thing," Macomber said, miserably. (2.43)
Macomber is changing his mind about hunting. Hearing the lion's roar all night doesn't empower him; it wears him down. But hey, we will be the first to admit that we would not be feeling to gung-ho after hearing that racket all night, either.
"You'll kill him marvelously," she said. "I know you will. I'm awfully anxious to see it." (2.50)
Here we see Margot's direct participation in the game of macho display. She wants Macomber to prove himself and she wants to be there to watch. Or is she being sarcastic? We can't tell if she is drawn to the violence, or disgusted by it.
There was dark blood on the short grass that the gun-bearers pointed out with grass stems, and that ran away behind the river bank trees. (2.92)
Macomber didn't count on the mercy-killing part of the hunt. Part of the code is that you can't leave a lion in misery, but that means you have to follow the blood trail and witness the gory mess you have caused.