My wireless keyboard works fine, but it's a bit dirty, and some "stuff" (I suspect my kids' toast crumbs) has got inside it. If you hold the keyboard up and tilt it from side to side, you can hear something rattling its way from one end to the other. I've read that the keys can be gently levered out individually, but is there any way to get the back off? Are there screw-heads hidden under the two rubber feet? Or will I be able to get the crumbs out if I just remove all the keys and shake it upside-down?