The speaker here is issuing a threat, but the last line changes what kind of threat it is. At first it sounds like plain aggression: don't touch me, don't speak, or I'll tear your throat out. The language is blunt and violent, with no softening and almost no punctuation to slow it down.
Then comes the twist: the speaker will attack "even if there was no threat at all." That admission suggests the danger isn't really out there. It's in how the speaker feels. Someone who reacts to harmless moments as if they were attacks is probably living in a constant state of alert, and the poem hints that this defensiveness has become automatic, maybe even beyond the speaker's control.
The mood is tense and raw, a little frightening, but also oddly vulnerable. The title, "Ancient Artifact," may point to an old, instinctive reflex, something primal left over from earlier times. The anger reads as armor, and the fear underneath it is what the poem quietly reveals.