Drat, drat, drat, drat, drat!
I am kicking myself. It was a rookie mistake and I should have known better.
I was working away on the heel flap of the Watermelon Sock when something twigged. All those stranded rows? The ones I was so proud of?
I had completely forgotten to adjust the size of the sock so that it would actually fit over the size of the foot for which it is intended. Stranding takes away a lot of the horizontal stretch in the knitting. Duh.