"Thallium is highly
toxic and was used in
rat poisons and
insecticides. Its use has been cut back or eliminated in many countries because of its nonselective toxicity. Because of its use for
murder, thallium has gained the nicknames "The Poisoner's Poison" and "Inheritance Powder" (alongside
arsenic)."
Just a note from wikipedia.
P.S. I've had them too. When at my last one I said to the Dr. who administered the test "Oh you mean rat poison." he somewhat snickered and said "Yes".
This was NOT meant to talk you out of it - just a hopefully humorous view of it.