The speaker tries to describe the feeling of being unable to speak, and reaches for a startling, grisly image: a chicken's head, cut off, its beak still opening and closing in the dirt. Nearby, the headless body keeps moving as if nothing has changed. The speaker says that's what having "no words" is like.
The comparison is split in two. The beak is the part that can still make the shape of speech but has no body, no breath, no purpose behind it. The body is the part that carries on with "the motions / of real life" but has lost its head. The speaker seems to feel both at once: going through daily life on autopilot while the voice stays disconnected and useless.
The mood is shocked and bleak, with a dark edge of humor. The poem itself comes up short, ending abruptly on "no words," just as the speaker does. The line breaks add to this, leaving the last two words stranded alone.