I had crossed the cable twice for no apparent reason. And what was worse, I didn't notice it until at least 25 rows later. I could have frogged down to before the mistake and re-knit. I could have ignored it and went on. Many very good knitters did indeed urge me to forget it and move on. I stewed and stewed over what to do, and then realized the fact that I was stewing over it meant I had to fix it. So, Cable Surgery it was.
Step One: Knit until you reach the stitches which comprise the cable. In this case, we are working a six-stitch, P1K1P1 cable. Slip all the cable stitches off the needle and ravel them all down past the mistake, then put the cable stitches on a dpn:
In this case, my dpns are quite a bit thinner than my working needle. It's probably better to have dpns close to your needle size, because you are going to be re-knitting your ravelled stitches and your gauge will be off if your needle size is too different. In this case, I was too lazy to hunt up different dpns.
Step Two: Using the closest loop from the ravelled stitches, begin re-knitting your cable:
Here, I am preparing to purl the first stitch of the six-stitch cable. Just like regular knitting, you bring the yarn forward to purl and take it to the back to knit.
Step 3: On the correct row, work your cable:
Step 4: Continue re-working each ravelled row, being careful to use the closest loop of ravelled yarn, taking each in order:
Here we have the first cable correctly re-worked. Now it's just a matter of working up the ladder, keeping track of each row as you work it so you can cable on the correct row. Note that I have quite a bit of looseness in the left-hand stitches. I fixed this by distributing the slack among the other stitches as I finished each row, by inserting a needle point into each stitch in turn, making each one a little bigger. The closer your dpn size is to your working needle size, the less slack you will have on the edge. This also means you will have less yarn to make your last couple of stitches, so you may have to do a bit of maneuvering to get the stitches on the needle. Make sure you don't twist your stitches as you make them.
Step 5: When you have re-worked all the rows, slip the stitches from the dpn back on to the working needle. You're good to go! A couple of tugs sideways and lengthwise helps reshape the stitches, and after a good wash and block, you probably won't be able to tell which cable got the surgery: What? You've never used your cat as a prop before?