On the second floor, in 1588, her son Henri III used not poison but a dozen men armed with swords and daggers to do away with his archrival, Duke Henri de Guise.
Swords are more effective on men than poison. 
mnli hypothesis: Swords are more effective on men than poison.  premise: On the second floor, in 1588, her son Henri III used not poison but a dozen men armed with swords and daggers to do away with his archrival, Duke Henri de Guise.