You hurl the boomerang used in the casting and speak ancient, thunderous words. The boomerang stops in midair in the middle of its flight with a burst of thunder. All creatures that can hear within 15 feet of the boomerang must succeed on a constitution saving throw, taking 5d10 thunder damage on a failed save, or half as much on a successful one. In addition, for the rest of the duration, all creatures that enter within 15 feet of the boomerang must succeed on a constitution saving throw or take 1d12 thunder damage. When the spell ends, the boomerang returns to your hand.