All bark and no ___ (intimidating but harmless)

Electric guitar's enhancer, for short3 Cain's brother4 "The ___ School Bus" (Ms. Frizzle's educational program)5 ___ booth (spot to click pictures at prom, perhaps)5 "... and so on," for short3 Sound bounce in a cave4 ___ one's own horn (brag)4 Big business, for short4