When you're an infant, the brain makes three dots and a line into a face; later in life, it turns a creak and a shadow into a ghost. Adults too often perceive bad luck as the work of a conscious (if vindictive) mind. You can resist it with logical thought, but the mind's default setting—what happens quickly, automatically, uncontrollably—is to believe its experiences were caused by living, thinking, feeling beings.

If you want to see how little the brain needs to trigger the sense that it's perceiving a person, look at the biomotion walker. All you'll see, literally, are a few lights moving on your screen. What you'll perceive, though, are people, and you'll be able to tell if they're male or female, angry or sad. Try it for yourself right here.

We are uncontrollably trigger-happy with our mental tools for perceiving objects as people. That can be a lot of fun. But along certain byways in robotics, it's getting a little creepy.