Actually, you wouldn't need animatronics to make it open. There are a number of things I've seen that open using springs. The system works something like this:
You just press a button and it opens up. The springs keep it from snapping open too fast. A clip under the button holds the movable pieces together. To close it you just close the pieces until they clip.
It's been a while since I've seen anything that opens like this. To see it used in a pred backpack would be totally awesome!