If we can rely on American Idol for one thing, it's to witness some of our favorite pop and rock standards get mutilated in increasingly graphic and elaborate ways, like some nubile brunette exchange student wandering unwittingly into an Eli Roth movie. It was Jason Castro who delivered last night's purest moment of armrest-clutching terror, an aural torture in two acts that first required him to channel Bob Marley's "I Shot the Sheriff," apparently as interpreted by a special-needs monkey. Predictably, the performance inspired some extra-vicious critiques from Simon Cowell. (We were a little surprised, however, that none of the take-downs involved the term "dredful," or his envy of the sheriff's sweet, silencing fate.)