Though originally intended to provide an insight into human psychological reaction to robotic design, the concept expressed by this phrase is equally applicable to interactions with nearly any nonhuman entity. Stated simply, the idea is that if one were to plot emotional response against similarity to human appearance and movement, the curve is not a sure, steady upward trend. Instead, there is a peak shortly before one reaches a completely human “look” … but then a deep chasm plunges below neutrality into a strongly negative response before rebounding to a second peak where resemblance to humanity is complete.

This chasm — the uncanny valley of Doctor Mori’s thesis — represents the point at which a person observing the creature or object in question sees something that is nearly human, but just enough off-kilter to seem eerie or disquieting.