1. To cut off the head; specifically, to remove the head of a foetus to facilitate delivery in cases of irremediable dystocia; to cut off the head of an animal in preparation for certain physiologic experiments; obsolete term.
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If it's done right, it isn't excessively cruel (or at least no moreso than any animal sacrifice for human uses). We used to decapitate our frogs - they were still alive, but couldn't process and pain.
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