What provokes the following response from Higgins? "Would the world ever have been made if its maker had been afraid of making trouble? Making life means making trouble. There's only one way of escaping trouble; and that's killing things. Cowards, you notice, are always shrieking to have troublesome people killed." He is defending himself for "making trouble" for Liza. He is accusing Liza of being a coward. He is defending his temper and tendency toward violence. He is railing against the cowardice of Freddy.