The little robot's big round eyes glow a happy green, and its antennae lean forward. "Hello, I'm Quasi!" it chirps to a small crowd at an exhibition held this past fall at Carnegie Mellon University, in Pittsburgh. "What's your name?"

"I'm Chelsea," calls out a young woman. Quasi swivels its head to face her and leans back slightly, as if to get a better view. "He's so cute!" Chelsea whispers to her friend, who also seems enchanted with the 76-centimeter-tall bot.

"Hi, Chelsea!" Quasi exclaims, giggling a little as its eyes flash purple-pink for a second. "Do you want to see my Halloween costume?" Chelsea says yes.

"Okay! Watch this!" The little robot's body suddenly goes rigid, its eyes glowing red. "Luke, I am your father," the voice of Darth Vader proclaims.

The onlookers, mostly science journalists, laugh nervously. Then the animated machine seems to relax, and its eyes revert to their friendly green hue. It resumes working the crowd, waving its knobby arms, cocking its head, swiveling its antennae like the ears of a dog.

While most robots are designed to serve a single dull, utilitarian function, Quasi's reason for being is charm. The machine's creators, all graduate students at Carnegie Mellon's Entertainment Technology Center, wanted to build a captivating character that would go well beyond the standard animatronic amusement park figures that spew out canned patter to bored preschoolers. They wanted to build a robot that would make people forget it's a robot.

To do that, they programmed Quasi to mimic the slightly snarky, moody personality of a 12-year-old boy. Quasi's five "moods" [see photos, " Mood Indigo"] are conveyed most obviously by the color of its light-emitting-diode eyes and antennae: green for happy, blue for sad, red for angry, yellow for confused, and purple-pink for embarrassed. Quasi's got lots of expressive moves, too: the bot hunches its shoulders, gesticulates with its hands, shifts its weight, and looks you straight in the eye.

All this is done so convincingly that you probably wouldn't even notice that Quasi's feet are bolted to a fixed base that houses 32 industrial off-the-shelf servos--2 for each antenna, 4 for each eye, and 24 for limbs and posture--that control the little robot's every move. Additional hardware, including microphone preamplifiers, a mixer, a sound processor, wireless audio receivers and transmitters, and four custom PCs that serve as Quasi's "brains," is stored in a separate case.