It's the cavity's ECHO,
the subsurface humidity.
Money Heist Season 3, Episode 8
There's an ECHO.
Money Heist Season 3, Episode 8
(SHOTS ECHO)
Westworld Season 3, Episode 8
but our war cries will ECHO through eternity.
Game of Thrones Season 2, Episode 10
( gunshots ECHO )
Westworld Season 2, Episode 10