That anomaly in the middle is me blinking. The NeuroSky MindWave Mobile can detect blinks. Also, if I hold my eyes in a squint, I can get the signal to oscillate quite a bit, so I suppose it can detect squinting too.
Now, NeuroSky doesn't hide the fact that they can detect blinks. In fact, it sends a special "blink detected" signal when this happens. But I'm worried that this device is just detecting the configuration of my forehead. It definitely is influenced a lot by the way my forehead moves, and I can't seem to correlate it with anything else, like how tired or awake I am.
On a positive note, I am quite pleased with the code I wrote to achieve a real-time brainwave (or more probably blinkwave) visualizer using node.js, socket.io, and an html canvas. Node.js listens for signals from the headset, sends then via socket.io to a webpage, which draws them on a canvas.