This is a simple tool for extracting unsafe bolts from a sport climbing route. It is so named because it's best at removing one-piece hammer-in bolts, which are nicknamed "carrots".
The device is basically a flat, square steel plate, about the size of your palm. It has a U-shaped slot extending from one edge to the center, and a threaded hole in each corner.
To use this, you slide the notch around the carrot's shaft, so that the plate lies between its head and the rock face. You then take four ordinary machine bolts, thread them into the plate's corner holes, and start tightening them evenly with a socket wrench.
As you tighten down those four bolts, their front ends start protruding out the back of the plate, pressing against the rock. That puts outward force on the plate, making it slowly pull away from the rock and take the carrot along with it.
This process is a lot slower than just hauling out a crowbar, but has a few advantages. First, since the killer applies force directly outward, it's far less likely to snap the bolt off inside its hole. Second, it can be used with very little leverage, which is a significant concern when you're dangling from a rope way up off the ground. The points of the four bolts do have an unfortunate tendency to mar the rock face, though care and skill can mitigate this.
I have a carrot killer sitting on my workbench. I've never used it. It's just there to look like a puzzling chunk of metal, so people ask about it and I get to tell them what it's called. Nothing gets a conversation started like a widget named after a sociopathic bunny rabbit.