Fed a body to an alligator.
It's best to do this near water to save time carrying the body. While standing near any dead enemy, follow the prompt to pick up their body and carry it to the nearest water. Almost all waterways contain alligators, even if they're not seen, and dropping a body in will usually make one appear and eat it. Killing an enemy near water can often make them fall into it, which will also unlock this achievement.