What deductive reasoning does Rainsford use concerning the type prey on the island?

Rainsford used his knowledge and experience to deduce that the game on the island was large and ferocious. He remarked on the condition of the area in which he deemed it was killed, and also commented on the weaponry the hunter used to being the prey down.

"Some wounded thing--by the evidence, a large animal--had thrashed about in the underbrush; the jungle weeds were crushed down and the moss was lacerated; one patch of weeds was stained crimson. A small, glittering object not far away caught Rainsford's eye and he picked it up. It was an empty cartridge."

"A twenty-two," he remarked. "That's odd. It must have been a fairly large animal too. The hunter had his nerve with him to tackle it with a light gun. It's clear that the brute put up a fight. I suppose the first three shots I heard was when the hunter flushed his quarry and wounded it. The last shot was when he trailed it here and finished it."