In the title, "Killer" is somewhat figurative, but may be quite true. When reading something about thatching, an old piece of equipment came to mind. It's a thatching blade which is basically like a rotary lawn mower blade with a spring attached at both ends. When I searched for spring and thatcher, I found a bunch of references to the Arnold Universal Power Rake. Nearly exactly like what I saw used back in the 80s. Here's a link first, so you can see what it is... http://content.sears.com/shc/s/p_10153_12605_07157777000P?keyword=rake If the link ever goes away, search for the Arnold Universal Power Rake. May not be the only one like it either. I found the Arnold one on Sears, Lowes and several other websites. When the thing is used - I don't want to call it a tool - it spins around and around at high speed. If you can visualize how fast a mower blade spins, you may understand that as the mower moves forward, the blade spins the springs so fast, that virtually no grass blade escapes getting hit. But devices like the Arnold Universal Power Rake, virtually shred, bruise, break and tear every grass blade, most of stems and even into the roots sometimes. When I saw the results left behind by one, the lawn area was like a huge area of massacred lawn. Only had to see someone use it once. Anyone else ever seen one of these in action. The only possible use I can see for this tool, is if someone sprays a lawn to kill it, intending to just overseed, and needs to pulverize the surface prior to raking and seeding. I have never seen another small device do so much damage to turf. The event I witnessed, was an old-timer retired from the turf industry trying it out on some condominiums where he had a landscape maintenance contract.