Robots become unsettling right before they become convincingly human

As a robot or animated face grows more human-like, people's comfort with it rises steadily — until it gets almost, but not quite, right. At that point comfort plunges into revulsion, then climbs back up again near perfect realism. Robotics researcher Masahiro Mori proposed the effect in 1970, decades before CGI and androids made it a hands-on design problem.

— Masahiro Mori, Bukimi no Tani Genshō (The Uncanny Valley) — Energy, 7(4), 1970