If a CGI monkey instead of Tom Hanks played the conductor in The Polar Express, monkeys would be afraid of it.

Princeton University researchers have come up with a new twist on the mysterious visual phenomenon experienced by humans known as the “uncanny valley.” The scientists have found that monkeys sense it too.
The uncanny valley, a phrase coined by a Japanese researcher nearly three decades ago, describes that disquieting feeling that occurs when viewers look at representations designed to be as human-like as possible — whether computer animations or androids — but somehow fall short.
Movie-goers may not be familiar with the term, but they understand that it is far easier to love the out-of-proportion cartoon figures in the “The Incredibles,” for example, than it is to embrace the more realistic-looking characters in “The Polar Express.” Viewers, to many a Hollywood director’s consternation, are emotionally unsettled by images of artificial humans that look both realistic and unrealistic at the same time.