James Martin/CNET

When you see a cat or dog, the wagging tail or arched back can immediately tip you off to the animal's mood. Can technology make it as easy to read people?

That's the idea behind the Necomimi, a pair of brain-wave sensing robotic cat ears made by Japanese company Neurowear. The fuzzy motorized ears are built atop headset technology created by San Jose, Calif.-based NeuroSky. It relies on electroencephalography from a single sensor placed on the forehead to read a person's brain waves and communicates with a nearby PC or Mac with a wireless USB plug-in to determine if a person is focused or relaxed. If the wearer is focused, the attached ears stay erect. When relaxed, the ears face down.

Earlier this year, Neurowear made a cutesey video of the ears that became a small hit on the Web, generating 1.6 million views (a lot of people could probably identify, as the girl in the video checks out an attractive guy, and her robotic ears move). Neurowear's original intent was to make only one pair, but after the gimmick attracted so much attention online, the company decided to produce a line of robotic ears.

Tansy Brook, a spokesperson for NeuroSky, visited CNET headquarters in San Francisco earlier this month to show off the third prototype of the ears and give me a chance to try them on.

My first question, naturally, was, "Do these things work?" I clipped the NeuroSky MindWave headset to my ear to place the brain-scanning sensor reader against my forehead. (The earlobe picks up the same ambient noise as the head, so the ear clip is used for noise cancellation purposes). In theory, brain states can be detected by measuring patterns of brain activity. This gadget claims to measure brain waves as an indicator of mood: if a person is concentrating, brain waves will be in the range of 12 to 30 hertz, NeuroSky says. If they are relaxed, brain waves will measure in the 8- to 12-hertz range.

In my case, the headset didn't fit, so the sensor had trouble picking up on my mood. However, when I held the sensor closer to my forehead to create a stronger connection, the ears seemed more responsive. For the most part, the ears stayed erect, which apparently meant I was focused. I tried relaxing to make the ears go down but found it hard to stay in control. Perhaps I couldn't fully get to a calm state during the interview because I was trying to multitask. Stephen Beacham, a CNET television producer, tried on the ears and had a much easier time getting them to switch positions. He even made the ears spin with excitement (impressive!).

Of course, whether the ears work is one thing. Whether people would ever wear them in public is another.

When I wore the furry ears out on the street, people stopped and stared, probably wondering if I was some wannabe cyborg Playboy bunny. When I asked them to try the ears on, they hesitated. Apparently, this sort of thing is more accepted in Japan--where fuzzy feline ears feature in otaku subcultures centered on anime and manga fandom--than it does on the streets of San Francisco.

Now playing: Watch this: Watch how robot cat ears can read your mood

The technology used in the funky ears represents a familiar course for advanced tech; once expensive and large, brain-scanning devices are becoming smaller and cheaper. And that opens the door to potential new consumer uses.

EmSense, another San Francisco Bay Area company, makes a headset that can measure how consumers respond to content like games and ads. But mobile brain-wave gadgets go beyond gauging consumer enthusiasm. Another California-based company, Neurovigil, uses a device called the iBrain to record sleep patterns. It may soon be used to identify a number of neurological conditions, as well.

Anyone can modify the NeuroSky headset; if you don't like cat ears, you can build one with devil ears. But designers and companies have been much more creative with their hacks, Brook said, adding that the headset is currently used in the Mattel Mindflex toy and is in use by 150 universities around the world for educational purposes.

It makes sense that the headset could be used to help people perform better. For instance, if you're an athlete training for an upcoming competition or a student wanting to measure how well you're concentrating on your work, you could use the headset to keep track of your mental state. My take on adding the ears is that they're interesting, but perhaps there's a reason humans don't have twitching tails. We don't really want people to be able to read our moods at a glance.