This is one of a series of limericks Asimov wrote about various poisons in 1984. Like the others, it appeared in the “Detectiverse” feature of Ellery Queen’s Mystery Magazine (the August 1984 issue, in this case). It has all the virtues and vices of Asimov’s limericks generally: it’s clever but not really rib-tickling, but at least it scans without much trouble.