This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Forensic Medicine
Which of the following is the 'ordeal poison' used by tribes of Africa? 
Select and explain. 
A. Physostigmine, B. Digoxin, C. Cocaine, D. Atropine
A: Physostigmine
Answer: A: Physostigmine 
Explanation: Physostigmine, also called eserine, is an alkaloid obtained from the Calabar or ordeal bean. The Calabar bean once was used by native tribes of West Africa as an "ordeal poison" in trials for witchcraft, in which guilt was judged by death from the poison, innocence by survival after ingestion of a bean. Ref: Taylor P. (2011). Chapter 10. Anticholinesterase Agents. In L.L. Brunton, B.A. Chabner, B.C. Knollmann (Eds), Goodman & Gilman's The Pharmacological Basis of Therapeutics, 12e.