I had an early Nexus phone (I forget exactly which one) that had a seemingly physics-defying ability to slooooowly (over the course of minutes) slide off apparently-flat-but-actually-slightly-not surfaces, when laid on its back. Not due to alert vibrations, either, but when entirely idle, or even turned off. I think Google accidentally made the back out of some kind of sci-fi ultraslick material or something.