I had been slowly knitting a needle at a time on the "Two Socks At Once" (or Parlor-Trick Socks) and trying to decide how to cast them off at the cuff. I wanted to use the "tubular bind-off", where the knitting just seems to magically end at the top. So I knitted the last few rows of the cuffs as "K1 P1" ribbing to set up for that.
I wanted to keep the two socks together as long as possible, so when I saw I was running out of yarn, I took the stitches from just one needle onto two needles.

Then, to do the tubular bind-off, I took the stitches of the inside sock onto two needles, so the purls were on one needle, and the knits were on a second needle. Here we are, partway around the sock. The bottom (pink) needles are the outer sock, and the upper (purple) needles are the inside sock I am binding off. You can't really see the bound-off part, but it is at the right side, under this profusion of needles.

And here is the inside sock, all bound off, with the outer sock stitches taken onto two needles. My SOP (Standard Operating Procedure) for doing the tubular bind-off is as follows: get out my diagrams that I always use and look them over. Feel confident and sure I remember and understand how this works. Start binding off with a yarn needle. Do the first several stitches backwards, meanwhile confidently progressing, sure I am doing it correctly. Realize that something doesn't look quite right. Pull the yarn back out again and put the stitches back on the needles. Start over -- this time I double-check the diagrams. I'm sure I'm doing it right. Find that I have somehow twisted one stitch, three stitches ago. Pull yarn back out to that point. Go off and do something else while I recover my temper. Come back and find that somehow the procedure has resolved itself in my head, and have no trouble for the rest of the sock!

And here we are, the ultimate test of handknit socks!

I have put up a few more pictures on the Double-Knitting Yahoo group.