Slide a 2.4mm black tungsten bead onto a size 14 1XL nymph hook and push it forward, but plan to set it at least a full bead-length back from the eye. The partridge collar goes in front of it.
Start brown thread and tie in the vinyl rib about a third of the way back from the eye, then bind it down to the rear, a little way around the bend.
Leave the thread hanging at about the midpoint, take three big open wraps to park it out of the way, then wrap the vinyl rib forward in touching turns to the midpoint; unwind the three wraps and tie the body off.
Tie in a brown CDC feather by the tip just in front of the body. The stem is delicate, so use light tension and hackle pliers.
Take two or three turns of CDC, tie off and trim; stroke the long barbs back and lay them roughly flat along the body.
Slide the bead back against the CDC, spin a small pinch of peacock Ice Dub on the thread and wrap a thorax slightly fatter than the CDC, right up behind the bead.
Wrap the thread over and in front of the bead, leaving enough room to hackle in front of it.
Tie in a Hungarian partridge feather by the tip in front of the bead, using the stem to help lock the bead in place, and take two or three turns of long-barbed hackle; tie off and trim.
Stroke the barbs back, build a small head, and whip finish without trapping fibers forward.
Clean up by pinching off the longest CDC barbs with your fingernails so the rear hackle is roughly body length.