Start black thread on a standard-length dry fly hook and leave a long tag hanging out before you wrap it down; that tag becomes the rib, so pull extra out first. Take the thread all the way back to the bend.
Park the tag out of the way and tie in eight or ten red hackle fibers as the tail, about a hook gap long. Pull them off the stem perpendicular to it so the tips stay in line.
Snip the butt ends off, leaving enough to serve as part of the underbody.
Catch in the white floss up front and wrap it down to the bend and back so you get at least two layers. Spin the floss a couple of times in your fingers if it starts spreading out, and let it lie flat over the back for a smoother body.
Tie the floss off up front with a couple of good wraps and trim the excess. Do not worry if the body is not thick or brilliantly white, the rib goes through it anyway.
Counter-wrap the black thread tag forward as the rib, about five evenly spaced turns. Spin it clockwise in your fingers first so it stands distinct instead of lying flat. Catch it off with two wraps and snip.
Tie in two small grizzly hackle tips as a down wing, about a body length long. A wrap up underneath will lift them if they are lying too flat, and a little splay is fine. Snip the excess.
Tie in one long grizzly dry fly hackle sized to the hook, leaving a bit of bare stem showing where the first wrap will land and turning the stem perpendicular to the shank so the first fibers splay out square. Smooth the head area first to give the hackle a good base.
Take four or five good turns of hackle, catch it off with two wraps and snip the excess as close behind the eye as you can get.
Pull the hackle back to open room, whip finish, poke your scissors in for any cleanup, and add the smallest drop of head cement.