Uncanny valley:
"The uncanny valley is a hypothesis in the field of human aesthetics which holds that when human features look and move almost, but not exactly, like natural human beings, it causes a response of revulsion among some human observers. The "valley" refers to the dip in a graph of the comfort level of humans as subjects move toward a healthy, natural human likeness described in a function of a subject's aesthetic acceptability."
The First Description of Ford Prefect
"He's not conspicuously tall, and his features are “striking but not conspicuously handsome.” His hair is wiry, almost a ginger color, and brushed backwards from the temples. His skin “seemed to be pulled backwards from the nose.” He rarely blinked, and he usually did only when surprised. He always smiled a bit too wide and too much, giving people the impression that he was about to “go for their neck.""