Great film! Scared the heck out of me, when I saw it on a small TV screen as a kid. I finally saw it again much later, at a Baltimore Science Fiction Convention (the Balticon). Larger screen. Still scary!
Jacques Tourneur, the director, fought against actually showing the
demon; he much preferred the
unseen evil, as being more disturbing. He lost out to the studio on that one, but Val Lewton had been had been in synch with his thinking, when he had him direct some the first of his classic 1940's horrors for RKO. Cat People and I Walked with a Zombie are the most famous, but here's a short clip from the third, lesser known, The Leopard Man, which demonstrates his approach: