This movie scared the PANTS off me when I was a little kid. It was released to theaters in 1979; I would have seen it a few years later when it played on broadcast television.
It made such a terrifying impression on me that I’m a little surprised I never developed even the mildest phobic response to mannequins. (I’ve met other adults for whom they are just too creepy.) They don’t bother me in the slightest. I feel the same way about clowns.