[Gorzaloon]

From a bit of organic synthesis work, I remember reading the warnings about blindness from osmium tetroxide...it "crosslinks" those numerous natural compounds (in the eye) that have lots of double bonds.

It is used as a contrast medium in electron microscopy for that reason, binding strongly to protiens. The most common consequence of breathing it is that its foul smell is the last thing one ever smells because it destroys the olfactory apparatus, even in small concentrations.

[Beaker]

OsO4.... You know that you've had way too much of organic chemistry when you see the molecule not by its name, but instead by it's resonance stucture- double bonded O's right down to the last electron. Either that or you realize that you are a nerd with a capital N. Osmium tetroxide is also good for ozonolysis.