One of the mysteries of the English language finally explained.
1In similative phrases denoting frantic, unthinking, and often futile activity, especially in "running around like a headless chicken" and variants.
2A person, group, etc., engaged in frantic but purposeless activity.
Late 19th century; earliest use found in Christian Union. From headless + chicken, with allusion to the phenomenon whereby a chicken can move about for a short time after decapitation, due to reflex activity of the nervous system.
headless chicken/ˌhɛdləs ˈtʃɪk(ɪ)n/
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