At the beginning of the story as Rainsford and Whitney travel by ship to their exotic hunting locale, Whitney tells Rainsford,
" 'The old charts call it `Ship-Trap Island. . . .A suggestive name, isn't it? Sailors have a curious dread of the place. I don't know why. Some superstition--' "
A little bit later Whitney expresses to Rainsford that he has an eerie feeling about the island and hopes that they are past it. All the information that he passes along to Rainsford is from the crew aboard their boat. Connell uses this information and the two men's conversation about the morality of hunting to foreshadow the events that occur shortly after the dialogue.
The author's technique in establishing a mysterious setting early on in his work is not unusual for action- or suspense-filled stories. In fact, even though this is an older story, it reads well with modern readers because it follows much of the same format of our contemporary horror and suspense flicks.
Rainsford and his friend were talking before he fell off the boat about the island they were passing. His friend told him that ship-trap was evil and avoided by the natives.
"OFF THERE to the right--somewhere--is a large island," said Whitney." It's rather a mystery--"
"What island is it?" Rainsford asked.
"The old charts call it `Ship-Trap Island,"' Whitney replied." A suggestive name, isn't it? Sailors have a curious dread of the place. I don't know why. Some superstition--"
"Can't see it," remarked Rainsford, trying to peer through the dank tropical night that was palpable as it pressed its thick warm blackness in upon the yacht.
"You've good eyes," said Whitney, with a laugh," and I've seen you pick off a moose moving in the brown fall bush at four hundred yards, but even you can't see four miles or so through a moonless Caribbean night."
A bit later in the introduction...we learn more about Ship-Trap Island through a dialogue between Whitney and Rainsford.
Do you think we've passed that island yet?"
"I can't tell in the dark. I hope so."
"Why? " asked Rainsford.
"The place has a reputation--a bad one."
"Cannibals?" suggested Rainsford.
"Hardly. Even cannibals wouldn't live in such a God-forsaken place. But it's gotten into sailor lore, somehow. Didn't you notice that the crew's nerves seemed a bit jumpy today?"
"They were a bit strange, now you mention it. Even Captain Nielsen--"
"Yes, even that tough-minded old Swede, who'd go up to the devil himself and ask him for a light. Those fishy blue eyes held a look I never saw there before. All I could get out of him was `This place has an evil name among seafaring men, sir.' Then he said to me, very gravely, `Don't you feel anything?'--as if the air about us was actually poisonous. Now, you mustn't laugh when I tell you this--I did feel something like a sudden chill.
"There was no breeze. The sea was as flat as a plate-glass window. We were drawing near the island then. What I felt was a--a mental chill; a sort of sudden dread."
"Pure imagination," said Rainsford.
"One superstitious sailor can taint the whole ship's company with his fear."
"Maybe. But sometimes I think sailors have an extra sense that tells them when they are in danger. Sometimes I think evil is a tangible thing--with wave lengths, just as sound and light have. An evil place can, so to speak, broadcast vibrations of evil. Anyhow, I'm glad we're getting out of this zone. Well, I think I'll turn in now, Rainsford."
The sense of foreshadowing in the conversation between Whitney and Rainsford sets the tone that something bad happens in the story. The name Ship-Trap Island is something that has a bad connotation among the sailors, and the sense that everyone is holding their breath as the ship sails around this place is evident.