WASHINGTON - The substance that's believed to be contained in letters that were sent to President Barack Obama and to Mississippi Republican Sen. Roger Wicker is ricin. It's a poison that has sometimes been lumped in with other bioterrorism agents, because it comes from a relatively common plant -- the castor plant that makes castor oil -- and because it seems easy to make.
But in fact, ricin has created far more scares than victims.
It's more of a targeted poison -- a tool for an assassin -- rather than something with which to attack a lot of people.
What makes it scary is that there is no known antidote -- and it is at its deadliest when it is inhaled. It isn't contagious.
One bioterrorism expert at the University of Maryland says ricin is "one of the least significant" biological and chemical terror agents. Milt Leitenberg also says in nearly all cases when early tests show the presence of ricin, it turns out to be a false alarm.
A draft of a 2010 Homeland Security Department handbook lists only one person killed by ricin. And that was a political assassination of a Bulgarian dissident in 1978. He was injected with a ricin pellet, by way of a specialized secret-agent-style umbrella.