There was a dagger specifically for finishing off wounded knights.
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It's called the misericorde, which is Latin for mercy. It was a pointed, edgeless dagger used by knights to deliver a final mercy blow to the mortally wounded. It had a straight and narrow blade with no cutting edge, made just for a quick death. It was used to deliver the “mercy stroke” to a knight so seriously wounded that killing would be a mercy.
The blade was designed to be thin enough to strike through gaps between armor plates to ensure an easy cut. You can see the picture on the right. It looks today like something we’d use to open letters rather than perform mercy killings.
