A phenomenon where humans will have an overwhelmingly negative response to objects that look almost, but not exactly, similar to a real human being. This reaction can go as far as vomiting and abject terror. The name comes from the shape of the graph of human likeness to positive response, which shows a strong dip when objects approach 100% human likeness. The effect was first written about by Japanese robotics professor Masahiro Mori.

There are several theories as to why this strong revulsion occurs, the most likely explanation being that a corpse also matches the concept of being almost-but-not-quite human, so evolution has trained us to avoid such objects.