Tanguin is the name of a poisonous nut and a method of torture. It formed the principal element of Madagascan justice from 1610 to 1861.
Ironically, although "tanguin" comes from the Malagasy word tanghena , or “truth”, it is the worst way for determining the truth I have ever heard.
This is a summary of the legal procedure to follow when there was insufficient evidence to convict a suspect:
(Amnesty International look away now.)
Anthropologists marvel at how this practice became accepted as law. Although no-one can be certain, in many shamanic cultures vomiting is considered not only a physical but also a mental expurgative, the equivalent to a confessional.
Extrapolating this mode of reasoning, the inability to fully bring forth, and therefore expunge, your secret shows that your guilt (and shame) is sufficient to allow the overdose to happen.
(With enough long words I can make anything sound reasonable.)
The active ingredient in tanguin is digitalin, a drug used to slow the heart rate. Tanguin resembles nutmeg and is still bought from stalls in Madagascar it can be used as eaither a cardiotonic or to induce vomiting. The locals, however, are more likely to buy tanguin for good luck, particularly if they are standing trial in court.
*Even though torture could last days, it was still relatively mild compared to Queen Ranavalona’s most popular execution techniques. ( ie: boiling the condemned at the waist until death).
George Macdonald Frasier The Flashman papers VI, Flashman’s Lady (1977) Barrie and Jenkins LTD
This French thesis has some fascinating rare source material.