—Adam, via e-mail
A. If you have never seen it before and not again since, one possible explanation for a combination of leg scratching and dragging would be simply what humans know as the limb “falling asleep.” This situation results from nerve compression, which can result in temporarily numbness, weakness, and/or paralysis, as well as that momentary peculiar sensation and, in some cases, pain. So the scratching could have been to relieve the discomfort, while the yanking of the limb around may have been a natural frustration-driven response to temporary limb paralysis.
If this happens repeatedly or frequently, I would recommend discussing it with your veterinarian, who might want to do a more detailed neurologic exam.