What are two metaphors and two similes in "The Tell-Tale Heart"?
Metaphors are authorial tools to highlight similarities between two things that cannot be literally compared. Similes are a subset of metaphors that specifically use "like" or "as" to make that comparison.
Consider the following phrase, which contains both a metaphor and a simile:
His room was as black as pitch with the thick darkness . . .
The metaphor is "thick darkness." Darkness can't literally be thick, as could a soup or pudding, but by referencing thickness, Poe emphasizes how impenetrable the black is. The simile is "black as pitch," comparing the darkness of the night with the darkness of sticky tar.
Simple simile and metaphor like the ones above are common across all writing, but authors such as Poe use both tools with sophistication, building mood, character, and plot. Here is another sentence containing both a simile and a metaphor:
When I had waited a long time, very patiently, without hearing him lie down, I resolved to open a little—a very, very little crevice in the lantern. So I opened it—you cannot imagine how stealthily, stealthily—until, at length a simple dim ray, like the thread of the spider, shot from out the crevice and fell full upon the vulture eye.
The metaphor is the "vulture eye," which describes the eye of the old man that the narrator seeks to murder. Describing his eye as a vulture's does not mean that the old man literally has eyes transplanted from a vulture, nor does it imply any physical resemblance in color, size, or shape. Rather, the phrase references the traits commonly associated with vultures: cruelty, opportunism, and enjoyment of death and decay.
The simile is "like the thread of a spider." Here, the comparison is more direct but still not literal. By saying that the beam of his lantern is "like" a spiderweb, he is emphasizing its thinness and fragility, although it is almost certainly not literally that narrow. However, he's also comparing himself to an animal, contrasting the scavenging vulture with his own spider-like patience as a hunter.
When the narrator claims that the old man "had the eye of a vulture -- a pale blue eye, with a film over it," he is using a metaphor. It isn't really a vulture eye in the old man's head, and so we know it must be figurative. He compares the old man's eye to a vulture eye because it makes him think of death, and vultures are very much associated with death.
The narrator also claims that the old man's eye has "a hideous veil over it." Again, it doesn't have a literal veil over it, but the narrator compares what is likely the old man's cataracts to a veil. We often think of a veil separating death from life, hiding death's mysteries from us (and yet they are so close and separated from us by something so thin), and so this metaphor also points toward the narrator's association of the eye with death.
The narrator describes what he thinks is the old man's heart beat (though it is really his own) as "a low, dull, quick sound, such as a watch makes when enveloped in cotton." This simile compares his heart beat to a ticking watch (often associated with death as well -- think of a person who is "running out of time").
Finally, the narrator describes the ray of light from his lantern as being "like the thread of the spider." This simile compares the thin ray of light to a spider's silk; it was such a very very thin ray that it seemed as slight as the threads that make up a spider's web. Spiders also typically have a negative connotation, and, in this case, it seems to add to the creepiness of what the narrator is doing.