"a prisoner who specialized in trapping rats for food."

This reminded me of my father's account of the time he spent in a French concentration camp in the foothills of the Pyrenees during WWII. Many of the inmates of the camp were Spaniards who had been there since the Spanish Civil War and had become adept at survival. He described awakening in the morning to the sight of rats hanging from the rafters overhead by wire snares that the Spaniards had set to trap them as they ran across the rafters during the night. The meat made a welcome dietary supplement.