The poem takes the old phrase "wolf at the door," which usually means poverty or hunger waiting just outside, and turns it into something sharper. Here the wolf is reduced to a single image: "a tooth of night." It is not the whole animal but one pointed edge of darkness, aimed at a table full of people.
The word "glut" matters. It suggests too much food, too much laughter, a party that has grown a little careless. The tooth is pointed "at any glut of mirth," as if the dark is watching for exactly that moment of excess. The speaker doesn't say they feel afraid, but the tone is uneasy and watchful. Judging by the images, the speaker seems aware that comfort is fragile, and that happiness at the table sits close to threat.
The mood is tense and quiet. With so few words and short lines, the poem feels like a sudden chill in a warm room.