Plural of bullhead; small catfish found in freshwater, or people who are stubborn and thick-headed.
From 'bull' + 'head', referring either to the fish's bony head structure or metaphorically to stubborn people. The fish gets its name from its large, broad head relative to body size.
Bullhead catfish actually have poisonous spines and can 'bark' or make grunting sounds—they're small but surprisingly tough, which makes them a perfect namesake for hardheaded people!
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