" ... Feral, from the Latin adjective ferus, wild, via bestia fear, wild animal. Generally held to mean having escaped from domestication, and having devolved back to a natural state.
Turner said, "It's like you've been sanded down to nothing but yes and no, and you and them, and black and white, and live or die. It makes me wonder, what does that to a person?"
"Life," Reacher said. "Mine, anyway."
"You're like a predator. Cold, and hard. Like this whole thing. You have it all mapped out. The four guys in the car, and their bosses. You're swimming toward them, right now, and there's going to be blood in the water. Yours or theirs, but there's going to be blood. "

― Lee Child , Never Go Back (Jack Reacher, #18)