Fall of the House of Usher, excerpt
By Edgar Allan Poe

The room in which I found myself was very large and lofty. The windows were long, narrow, and pointed, and at so vast a distance from the black oaken floor as to be altogether inaccessible from within. Feeble gleams of encrimsoned light made their way through the trellised panes, and served to render sufficiently distinct the more prominent objects around; the eye, however, struggled in vain to reach the remoter angles of the chamber, or the recesses of the vaulted and fretted ceiling. Dark draperies hung upon the walls. The general furniture was profuse, comfortless, antique, and tattered. Many books and musical instruments lay scattered about, but failed to give any vitality to the scene. I felt that I breathed an atmosphere of sorrow. An air of stern, deep, and irredeemable gloom hung over and pervaded all.

Which words from this paragraph help create an unsettling mood?

trellised panes
sorrow, failed
instruments, atmosphere
oaken floor

It could have been an atmosphere of joy or happiness, but the author made it clear that the place was filled with sadness in his description. The fact the narrator was able to sense it shows that even visitors felt uneasy while in the house. It affects readers as well.

"Many books and musical instruments lay scattered about, but failed to give any vitality to the scene."

Because of the sorrowful atmosphere, not even the books or musical instruments in the house could successfully give it any life. Therefore, the word "failed" is used in a very serious context. Again, the narrator could sense it, which disturbed him (and readers).