US /baʊns ɔf ðə wɔlz/
・UK /baʊns ɒf ðə wɔ:lz/
Because the rattle is hollow inside, sound waves can bounce off the walls and echo.
Because the rattle is hollow inside, sound waves can bounce off the walls and echo, the same way shouting in a cave amplifies the sound.
From the voice to the look, the bio-exorcist seems to bounce off the walls in his every moment on screen.