Humans are "pathological anthropomorphizers," Winfield says. And that puts us at risk of becoming emotionally attached to a machine that can't reciprocate. It's the sci-fi equivalent of a one-sided friendship (or, possibly, robomance) with all of the corresponding social costs. When Winfield and his colleagues drafted ethical guidelines for creating robots in 2010, they included a restriction on deceptive systems. A robot's appearance, they wrote, should expose its mechanical form. "You should always be able to pull the curtain aside to reveal the machine," says Winfield, "just like Toto did in The Wizard of Oz."