Ten to twenty minutes after exposure, the body’s muscles begin to spasm, starting with the head and neck. The spasms then spread to every muscle in the body, with nearly continuous convulsions, and get worse at the slightest stimulus. The convulsions progress, increasing in intensity and frequency until the backbone arches continually. Death comes from asphyxiation caused by paralysis of the neural pathways that control breathing, or by exhaustion from the convulsions. The subject will die within 2–3 hours after exposure. At the point of death, the body “freezes” immediately, even in the middle of a convulsion, resulting in instantaneous rigor mortis.

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