What clues at the start of "The Most Dangerous Game" foreshadow danger ahead for Rainsford?

The first intimation of danger on the island occurs before Rainsford even swims to shore. He hears the cry of an animal being hunted; it is a piercing sound of an animal with which Rainsford is not familiar.

When Rainsford gets to shore and begins to explore the island, he finds empty gun shells. He assumes the gun was used to hunt the animal whose cry he did not recognize. Rainsford is puzzled as to why a hunter would use a small gun to hunt a large animal.

There is only a single house on the island, a looming, foreboding structure. General Zaroff's assistant, Ivan, is a huge person who is mute.

All of these details add up to masterful foreshadowing of the horror that Rainsford is to face. He discovers the horror while dining with General Zaroff and listening to the general describe his hunting habits and his prey.