Mount the rear hook of the articulated pair and dress it full: a marabou plume, schlappen, and a few strands of flash trailing past the bend for a breathing tail.
Connect the front shank to the rear hook with heavy wire or braid, binding it firmly along the shank and cementing the joint so the rear rides close.
Build a dense brushed body up the front shank, picking the fibres out as you go for bulk.
Tie in pairs of Sili legs along the body so they kick to the sides.
At the head, spin or stack a big deer-hair or Laser Dub wedge and trim it flat-faced; this water-pushing head is what gives the fly its heavy wobble and thump.
Add the 3D or dumbbell eyes, whip finish and cement.