To my eye, I do not see any build up or trace of foreign material on
the bottom of the wok. Thats the mystery. Splatter would be the
obvious culprit; however, since it takes a while to clean the stove, it
has made me extra careful with putting things into the wok. Another
guess I have had is that, when I heat up the wok, and then place some
food or liquid into it, the resulting change in temperature causes
something to flake off the bottom. When the wok cools enough for me to
clean it, nothing will come off because it takes heat to cause it come
off in the first place. Maybe what I need is what do I do to the
bottom of the wok to prevent this from happening?