What is personification and how is it used in "The Tell-Tale Heart"?

The literary device personification is when a writer gives typically human characteristics to non-human animals or objects. For example, describing a "furious thunderstorm" would be personification, because the phrase suggests that the thunderstorm has human emotions and can feel fury. 

Abstract ideas are often personified as well. For example, the concept of death or dying is often seen in literature as a human figure in a long, black, hooded cloak, carrying a scythe.  

The most important example of personification in the short story "The Tell-Tale Heart" is the personification of the old man's "evil eye." Though the narrator never describes the eye as having a human form or doing human things, he does see it as a separate being from the old man himself. The narrator says,

"it was not the old man I felt I had to kill; it was the eye, his Evil Eye" (paragraph 5).

This quote shows that the narrator sees the eye as having some kind of sinister purpose, separate from the old man, whom the narrator claims to love and sees as an innocent bystander to the eye's evil.

The narrator elaborates further on the evil quality of the eye, comparing it to, 

"the eye of one of those terrible birds that watch and wait while an animal dies, and then fall upon the dead body and pull it to pieces to eat it" (paragraph 3). 

Clearly, the narrator sees the eye as capable of great evil and perhaps even thinks it intends to harm him - two things that only humans are capable of plotting to do. 

There is, I believe, just one example of personification in this story. Shortly after the narrator describes the moments following when his finger slipped on the lantern and made a small noise heard by the old man, he describes what he believes the old man to be thinking since he feels he can relate. He believes the old man has been trying to reassure himself that the noise he heard is nothing to be afraid of. However, the narrator says that his reassurances are in vain "because Death, in approaching him had stalked with his black shadow before him, and enveloped the victim." Here, death is personified and given consciousness and intention, as well as the ability to approach its victim and cast its shadow upon the victim's body and soul.

This makes death seem that much more frightening, as though it considers its victim and "stalks" him ("stalking" never has a positive connotation); it makes death menacing and intentional, and it seems that this is how the narrator perceives death to be. He has no problem with the old man except his "vulture eye"—likely the result of cataracts, a malady associated with the elderly—and his association of the eye with vultures, which are associated with death. Therefore, it seems as though the old man is a reminder to the narrator of his own mortality (his obsession with time is also a clue to this), and so it is actually the narrator's own death that frightens him so much. He must kill the old man so that the old man can no longer remind the narrator that he, too, will one day grow old and die. Thus, the narrator's personification of death shows us how he views it.