Horror films have primed us to fear a lot of usually pleasant things, from clowns to dolls. When did a child's play toy start giving us the creeps?
As it turns out, doll faces have the ability to unsettle us at the most basic level. Humans are innately social creatures, so our brains have evolved to read faces for signs of emotion, intent, and potential threat. As dolls become increasingly realistic, our brains recognize their features as human-like...but not quite. The fact that their faces don't convey emotion just throws us off.