"I'm guessing he works with mercury. Just a guess, though. :)"
I've not worked with mercury for many years now, so the effects should have worn off. But, yes, I have worked with significant amounts of metallic Hg and its compounds in a previous life. My degree was in chemistry and, of course, we took appropriate precautions with the chemicals we used.
Mostly crypto and number theory these days. In the past, I've been employed as a molecular spectroscopist, a nuclear physicist, a roboticist and a geneticist. I still dabble in spectroscopy and astronomy.