In a way that shows a tendency to make petty criticisms; in a fault-finding manner.
From captious plus the adverbial suffix -ly, which converts adjectives to describe how actions are performed or states exist.
When someone responds captiously to your ideas, they're doing what linguists call 'negative pragmatics'—using language not to build understanding but to trap and criticize, which is why it feels so different from constructive feedback.
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