Most recently, moviegoers complained about the near-realistic depiction of humans in Disney's 3-D flick "Mars Needs Moms."
A theory called the "uncanny valley" says we tend to feel attracted to inanimate objects with human traits, the way a teddy bear or a rag doll seems cute. Our affection grows as an object looks more human. But if it looks too human, we suddenly become repulsed.
Instead of seeing what's similar, we notice the flaws - and the motionless eyes or awkward movements suddenly make us uncomfortable.
"Mars" may have plunged to the bottom of this valley of fear.
"People always comment on things feeling strangely dead around the eyes," said Chuck Sheetz, an animation director of "The Simpsons" and a professor at the University of California, Los Angeles. "If it gets too literal, it starts to feel false or has a strange effect."
Skin texture that is slightly off can especially leave people feeling unsettled, said Patrick Markey, a psychologist and director of Villanova University's Interpersonal Research Laboratory.
The near-realistic animation style championed by producer Robert Zemeckis uses motion-capture technology, where actors are covered with dots and skin suits and have their performances captured on computer. The dots provide the frame, and the rest is filled in with computerized graphics.
"Mars" creates humans that are more realistic and detailed than Zemeckis' earlier attempts in such movies as "Beowulf" and "The Polar Express" - which were also criticized for inviting this discomfort. The greater detail might have made things worse.
Doug McGoldrick, who took his two daughters to see the movie, said the faces of the main characters "were just wrong." Their foreheads were lifeless and plastic-looking, "like they used way too much botox or something," said the 41-year-old photographer in the Chicago suburb of River Forest, Ill.
Marc Kelley, a 32-year-old pastor in Allegan, Mich., who went with his two young children, said he found the renditions of characters "all annoying in their own way."
Indeed, when the mother of the main character Milo mentioned the word "zombies" at the start of the movie, it conjures up a feeling that the characters themselves are undead.
Animation experts say the key to success is to be only authentic enough to tug at our heart strings.
The best example of this was "Avatar," the 2009 blockbuster that made $2.8 billion in theaters worldwide. The humanoid, but blue-bodied Na'vi were alien enough not to trigger our inner rejection mechanism.
"My own personal opinion is try to stay away from photo-real with a human," said Greg Philyaw, the business development director at Giant Studios, which captured the performance of human actors for their digital re-creation in "Avatar." ''Subconsciously you know what you're looking at isn't quite right."
The Walt Disney Co., by its actions, has already voted against the super-real animation format.
Last March, it said it would shut down the Zemeckis-run company ImageMovers Digital, which made "Mars," to cut costs. Several months ago, Disney also nixed a plan to fund and distribute Zemeckis' "Yellow Submarine," a half-finished work he is now free to shop to other studios.
Disney declined to comment for this story, and Zemeckis declined interview requests through an agent.
"Mars" had an estimated $150 million production budget, but has brought in just $34 million globally since its March 11 opening.
To be fair, there were other problems besides being visually unnerving.
For one, it appeared to be marketed at young boys who are interested in science fiction but also are closely attached to their mothers. That is a small group to begin with and neglects dads and daughters. Some young children also got scared about the plot involving mommy abduction.
"Mars" also came just a week after Paramount's 2-D animated movie, "Rango," starring Johnny Depp. Instead of appealing to fans because of the increasingly popular 3-D format, "Mars" may have annoyed theatergoers faced with higher 3-D ticket prices.
"If a movie's unappealing and you're trying to charge a higher ticket price for it, it makes it even less appealing," said Brandon Gray, president of tracking company Box Office Mojo. He noted that "Mars" had the lowest opening weekend for a wide-release 3-D movie ever.
Maija Burnett, associate director of character animation at California Institute of the Arts, took a broader view, even though the school teaches about the pitfalls of the "uncanny valley" in class.
"There's a continuing attempt to explore what the boundaries are within (computer generated) animation," she said. "Every film that uses this is one important step along the way."
In the "uncanny valley" theory, the valley isn't bottomless. As things grow more realistically human, our affection starts increasing again, climbing out of the valley on the other side. In other words, increasingly sophisticated animation might stop creeping us out and start fooling us.