I got the first version to work. Here's the demo video:

There are several things there. I have the control board with the battery and accelerometer sitting at the top of my head -- this is obviously suboptimal, especially during rain. I suppose I can hide most of the electronics and the battery inside the ears themselves -- there is enough room for that. But the accelerometer has to stay. Or I could move the whole thing to the side, making it look like a bluetooth headset or something -- I would just need to switch the accelerometer axes then. I need to sleep on that.

Second thing, the range of movement is really limited. Those tiny servos don't really have enough strength to squash the material of the ears enough to flatten or perk them completely. I used those little guys, because I was afraid about space, but turns out that there is a lot of room inside those ears, so I might try with 9g servos next.

Third, they make noise. Since constant buzzing would be annoying and would drain the battery fast, I'm actually switching the servos off (by disabling PWM signal) when they are not changing the ears position. I only enable them for 600 milliseconds when they need to move. It would be much cooler to have them move fluently all the time, but not with those servos.

Fourth, I guess I could attach them to a hat -- then there would be no problem with hiding the electronics, and I could even have a larger battery.

Fifth, right now they only react to the head position. I need to experiment with tracking how fast I'm moving, and make them move based on that too -- make them droop when I'm not moving, and perk up when I make a sudden move with my head. Also, twitch them randomly when they are perked up.