Answer :
The following details from the narration show that Rainsford is an experienced hunter and outdoor enthusiast :
C. Some wounded thing, by the evidence a large animal, had thrashed about in the underbrush;
Rainsford's experienced eye could make out a wounded animal in the closely knit web of weeds and trees.
D. the jungle weeds were crushed down and the moss was lacerated; one patch of weeds was stained crimson
Rainsford noticed that some weeds were crushed down. This can only happen due to the weight of a wild wounded animal. He also noticed that the moss was torn at certain places and a patch of weeds was stained crimson from the blood of a hunted animal. Being an experienced hunter, Rainsford could pick up all these signs of a hunted prey.
E. A small, glittering object not far away caught Rainsford's eye and he picked it up. It was an empty cartridge.
Rainsford was a highly skilled and experienced hunter so he could not help but notice the empty cartridge lying near the wounded animal. He could easily recognize it from years of hunting experience.