GB, also known as sarin, is the nerve agent that killed 12 and injured 5,500 when cultists released the chemical in the Tokyo subway system in 1995. A deadly dose on the skin is 1,700 mg (about 0.06 of an ounce).
VX, another nerve agent, is even more deadly, with a lethal skin dose estimated at 10 mg (0.00035 of an ounce, a tiny pinpoint).
Mustard agent, also called blister agent, causes burning or blistering of the skin, lungs and mucus membranes. Used by both sides in World War I, it can blind or kill a victim. Often it causes tissue damage, with death resulting in a few days or weeks.