We gotta hand it to actor Jeremy Piven: 'mercury poisoning,' unlike 'exhaustion' or 'dehydration,' is an excuse we've never heard from a celeb. Let's help diagnose him—what could have caused it?

Well, there are a few common causes: too much of certain types of fish from polluted waters, like tuna and swordfish (a sushi binge, perhaps?), old-fashioned dental fillings, and—according to the NYU website—"fluorescent light bulbs, batteries, mercury switches in thermostats and even sneakers that light up."

Apparently, mercury has contaminated all levels of the food chain, including ducks and turkeys and chickens. Why, last January, the New York Times found high mercury levels in Manhattan-area tuna sushi. Run!

The side effects? They vary depending on the type of exposure, but range from kidney/neurological damage, tiredness, tremors, and problems with vision, speech, and hearing. Also: the total and complete inability to act, especially on Broadway.

Piven may well be going through "chelation therapy" right now, a process that rids the body of mercury. Don't worry, though: mercury poisoning is usually reversible.