a sound must first be emitted before it can reflect off of a surface
audible_sound is not wave_propagation. audible_sound is wave_propagation. making_crashing_sound is not sound_emission. sound is wave_propagation. making_splashing_sound is not sound_emission. sound is not energy. making_splashing_sound is sound_emission. sound is not wave_propagation. making_crashing_sound is sound_emission.