Yesterday, an envelope addressed to Senator Roger Wicker, Republican of Mississippi, was found to contain a white granular substance that was identified as ricin. Today, a similar letter addressed to President Obama was found. These envelopes were intercepted off-site--they never got anywhere near their targets--but as a precaution, Capitol Police have shut down mail service until they can figure out what's going on.

In the meantime, let's talk about ricin!

How poisonous is it?
Oh, man. Very. It's dangerous in just about any way it gets into your system, though ingesting (eating) it is about the least dangerous way. Injecting or inhaling requires about a thousand times less ricin to kill a human than ingesting, and that's a very small amount indeed. An average adult needs only 1.78mg of ricin injected or inhaled to die; that's about the size of a few grains of table salt--which ricin resembles visually.