The answer is human experimentation, but how we get there is kind of complicated.

[ Sam doesn't respond, just eating his sandwich, but for lack of anything else to talk about Drake shrugs and goes on. ]

I knew this guy from my time in prison, Pogo. He was a dealer... called me one night from the trunk of a car and I heard him get executed. But he told me what he was seeing out the tail light while he was in there, so I knew where he was buried. He had something on him that night, a bad batch of drugs that had caused a massacre. Or that's what I thought.

Anyway, looking into it I got shot. Almost didn't make it, but the guys who wanted the leftover drugs brought me to somebody who was able to turn me into a zombie so I didn't just die.

[ You still with him, Sam? And no, he's not shitting you. ]