I think it snapped in my briefcase. It was fine the last time I worked on the project yesterday. Luckily, only one broke. I pulled the needles out of the sock, flipped the needles around, and was able to continue knitting.
Disaster averted, as I thought I'd have to sit for an hour without a project. Later, I will need to pick up a replacement. Or maybe I can find a very small pencil sharpener?