It may be the most perennial of operas but in the public mind there is only one Tosca. Never the sweetest of voices or natures, Maria Callas brought veracity to a grubby plot and ferocity to its apotheosis. Groped by the sleazebag Scarpia, who has arrested and tortured her artist husband, Tosca grabs a fruit knife and stabs him dead. Callas, on stage, would strike so hard with the plastic prop knife that she drew blood from Gobbi, her regular partner, and gasps from the audience, who thought she had really killed him.

---Norman Lebrecht, The Life and Death of Classical Music