What's sexy about the spectacle of bullfighting is the tension among the matador, the bull, and the audiencegore and animal cruelty notwithstanding. What's sexy about the tension of Andrea Del Conte's rapturous 10-person Flamenco Fiesta at the modest Thalia in Sunnyside is that here the theater's the bullring, the dancers are the matadors, and we're the bulls. Oscar Valero, special guest dancer from Valencia, displays inordinately swift footwork, teasing the fine line between theatricality and control. When Del Conte takes the stage midshow to perform her coy solo, wielding castanets and wearing a splendid white-ruffled, long-tailed gown, this virtual bullring feels more like a cabaret. Vocalist Alfonso Cid leads the flamenco quartet; his voice, characteristically resonant and pained, could cut flesh.