I found this explanation in a Knitty pattern…maybe this will help. This is the site:
http://www.knitty.com/issuesummer06/PATTknucks.html
and these were the instructions, but they are for crochet, even though the pattern was knitted.
[I][FONT=Verdana]How to crochet your very own crab stitch edging, [/FONT][/I]
[I][FONT=Verdana]even if you’re really really scared.[/FONT][/I]
[B][FONT=Verdana]Story [/FONT][/B][B][FONT=Verdana](feel free to skip)[/FONT][/B]
[FONT=Verdana]I have this wonderful zip-up sweater that I’ve been wearing for years, and I could not for the life of me figure out what the edging was. It was a lovely, thick corded edge. It wasn’t until I started looking for an alternative edging for a cuff that I found out it was [B]crab stitch[/B]. At first, I didn’t get it. I tried crocheting backwards – and it just looked like crochet! Most of the instructions I found did not explain the little twist you need to do to make it work. So here you go, crab stitch tutorial. Try it on your next project! [/FONT]
[B][FONT=Verdana]Attributes[/FONT][/B]
[FONT=Verdana]Crab stitch is also known as reverse single crochet or shrimp stitch. [/FONT]
[FONT=Verdana]It gives you a thick but light, decorative corded edging. [/FONT]
[FONT=Verdana]You can work it on a crocheted or knitted fabric. [/FONT]
[FONT=Verdana]It’s CROCHET, so you need a hook. Got that, knitters? [/FONT]
[FONT=Verdana]Firm up the edge of your work, keeps it from rolling. [/FONT]
[FONT=Verdana]I found my cuff edge tight at first, but it stretched nicely (in wool) after a few wears. You want to do it pretty loose.[/FONT]
[B][FONT=Verdana]Technique (real low-tech-like, for baby crocheters) [/FONT][/B]
[FONT=Verdana]I like to work this edging on a row of single crochet. So first, I cast off loosely in single crochet. [/FONT]
[FONT=Verdana]At the end of your row/round of single crochet, do not turn your work. You will be working from left to right. Do one chain stitch. (not illustrated)[/FONT]
[FONT=Verdana]**[/FONT]
[FONT=Verdana]Insert the hook in the first stitch to the right. Ok, in this photo it’s not actually the first stitch, because I’ve done some already. But you see how to insert the hook through two loops on the top there, to the right of your working yarn. [/FONT]