U.S. counterterrorism officials say the Yemen branch of al Qaeda is trying to produce the lethal poison ricin. For over a year, the al Qaeda affiliate has been trying to obtain large quantities of the castor beans from which the poison is derived, according to classified intelligence reports. A speck of ricin can kill if it is inhaled or if it enters the bloodstream. Evidence indicates the group wants to pack the poison around small explosives and detonate them in an enclosed area, such as a shopping mall or a subway station. But the al Qaeda branch seems to be having trouble developing ricing into an effective weapon. The poison is not absorbed easily through the skin and loses its potency in dry, sunny environments like Yemen.