A speaker opens a door, ready to spit out some kind of mockery, and then finds that their mouth is dry. That's the whole scene, and the poem's strength is how little it says. The gesture of contempt is set up, then it fizzles. The speaker has the urge to hit back, but the body won't cooperate.
The short lines and tiny words ("the," "in," "my") break the sentence into pieces, so we move through it slowly, almost hesitantly, much like the speaker at the threshold. The door suggests a moment of confrontation or a step into something new, though the poem never says who or what is on the other side. Judging by the ending, the speaker may feel nervous, powerless, or simply emptied out. The mood is tense and deflated at once: anger without a voice, defiance that comes up short. The final word, "dry," leaves a quiet, uncomfortable stillness.