Making quick, chattering sounds; trembling or shaking, often from cold; nervous talking.
From Old English 'ceoterian' meaning 'to twitter or chatter.' Related to 'chitter-chatter.' The word evokes the sound it describes—it's an onomatopoeia. Used since medieval times for both animal sounds and human trembling.
Animals chitter for different reasons—squirrels do it to warn others, primates do it for social bonding, and humans often chitter their teeth when terrified, which is why the sound is universally associated with fear and cold.
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