Counterweight Catapult

I slipped away from the napkin pile and stalked down to the far end of the counter where the staff duck through. Right there was a heavy wooden flip-up pass-through hatch balanced by a hefty brass counterweight on a pivot arm! I grabbed the brass slug, braced my feet against the fluted laminate kickplate, and shoved it straight down with frantic glee. WHOOSH-CLACK! The thick wooden counter slab flew upright like an anti-aircraft barrier, clipping my tail and launching me backward into a stainless steel bus tub full of clean butter knives. What magnificent leverage!