The human race has only one really effective weapon and that is laughter. The moment it arises, all your irritations and resentments slip away, and the sunny spirit takes their place.

The quotation presents laughter as a uniquely human form of power: not a weapon that harms, but one that disarms hostility—within oneself and between people. Twain frames laughter as an emotional solvent that loosens “irritations and resentments,” replacing them with a “sunny spirit.” In this sense, humor becomes both psychological medicine and social strategy: it interrupts cycles of anger, punctures pretension, and restores proportion. The line also reflects Twain’s broader satirical outlook, in which comedy is a serious instrument for coping with human folly and for resisting cruelty or self-righteousness without resorting to violence.