Seems like four, five times a week some chunkhead hunkers down hard with his spurs on. When I got to the office that night there was one waiting--a bad one, Spanish rowels--and Jake was sprawled in my chair, picking his teeth with my spare scalpel. I patched up the chunkhead, took the scalpel from Jake and rinsed it off and watched him suck his teeth for a while. It began to look like he was going to be stubborn. So finally I said: "Say, Jake." He grunted. "Jake," I said, "I think I've got that dingus figured." He snuck a glance over at the desk so I knew he knew what I meant, but he was busy pretending that wasn't what he came to talk about. "I think it's a gun that can read minds like a gypsy," I said. Jake still looked bored, so I took the umbrella handle out of the rolltop and waved it at him. He dove off the chair and started rolling for the door. "You damn fool," I said, "it won't go off." I was reasonably certain it wouldn't, but I laid it back down by the disk gently anyhow and sat in the chair. I've only got the one chair, on the theory that anybody who isn't bad enough to lie on the table is well enough to stand. Jake edged over and stood like a short-legged bird on a bobwire fence. "It kin whut?" he said. "It can read minds," I said. "You were going to bash those bones. The gun knew it and trained square on your head. You remember?" He remembered. "And those Indians," I went on. "You remember them? The left side of the head on each of them was blown off." I hauled down a roller chart of the human skeleton, first time I'd done that since I don't know when. "This up here is the brain," I said. "We don't know a hell of a lot about it, but we do know it's like a whole roomful of telegraphers, sending messages to different parts of the body along the nerves. They're like the wires. This left hemisphere--right here--sends to the right side of the body. Don't fret about why, the nerves twist going into the spinal cord. "Okay. We know, too, that the part of the brain that sends to the arm is right here, in the parietal lobe. Right under the chunk of skull that was shot off on those three Indians." "Shaw," Jake said, perching on the table. The old billy-goat was beginning to get impressed, even if he didn't have any notion of what I was talking about. * * * * * I didn't have exactly much notion either, but I kept on. "The brain works by a kind of electricity, same kind as in the telegraph batteries at the depot. This gun," I tapped the umbrella handle and Jake started off again, but caught himself, "has some sort of detector, a galvanic thermometer that senses electrical messages to the nerves." From here on in it was pure dark and wild hazard. "Obviously," I said, "whenever one of those signals goes from this cerebral motor area here in the left hemisphere down to make the weapon hand move, it must be a special signal this gun was built to catch. Just like a lock is made for one particular key.