Foreshadowing is a literary device in which a writer suggests or hints to the reader at something that is yet to come out into the open. It is a technique that helps builds suspense. Four instances of foreshadowing are as follows.

Marston's death by poisoning is called "not a natural death" by Dr. Armstrong. At this point, everyone gathered on the island very much wants to believe it is a suicide, but Dr. Armstrong's words foreshadow the strong possibility that it is murder.

An important foreshadowing of death comes in the following passage:

Downstairs in the dining-room, Rogers stood puzzled. He was staring at the china figures in the centre of the table. He muttered to himself: "That's a rum go! I could have sworn there were ten of them."

Every loss of a little Indian figurine in the mystery foreshadows a murder.

In his bedroom, Justice Wargrave takes out his false teeth as he gets ready to go to sleep. We learn that

It was a cruel mouth now, cruel and predatory.

This foreshadows that Justice Wargrave is putting up a false front and is not what he seems—as we will find out.

Finally, remembering his guilty past and ruminating in his room at night, General Macarthur thinks,

Best of an island is once you get there—you can't go any further ... you've come to the end of things.

This foreshadows that the people mysteriously invited to the island are coming to their own ends.

Christie uses this chapter to gradually build a sense of foreboding and unease. Everyone on the island has a guilty past with something to hide. It's becoming more and more obvious that terrible things are going to happen.