Tough to tell what's crazier: that we expect more precocity from our young rappers than we ever have, or that they actually keep delivering. When 20-year-old Chance the Rapper's sophomore mixtape, Acid Rap, dropped in May, it landed like a tie-dyed dart on some throbbing nerve we didn't even know we had. The album is hallucinatory and unnervingly developed, flitting between gloomy ruminations ("Pusha Man") and calypso sway ("Favorite Song"). Chance is a braggart, but his nasal, acrobatic virtuosity isn't just meant to launch boasts. His confessions — about childhood nostalgia, about the trauma of watching a friend die — are delivered like flicks to the forehead; they're meant to keep us alert and slightly off-kilter. When he performs, expect to feel both coddled and thrillingly, unrelentingly prodded.