Oh, it's one of the fake Questions Frankie and Benjy try to come up with so they don't get into trouble... "What's yellow and dangerous?" In the end though, they went with Bob Dylan.
Incidentally, in the wikipedia entry for the Answer, they read waaaay too much into the yellow question.
Interestingly, I looked up molybdenum, number 42 on the periodic table, and it's sometimes used to make pigments - yellow-orange pigments. eek Freaky...
