Wow that perfectly explains something that happened almost 40 years ago - to wit, was getting a ride home after school in buddies car, windows down about 95%, we're chatting listening to radio etc when he picks up a spark plug (from his ashtray? cupholder? I forget) and throws it out his drivers side window. Except it hits the post and bounces back into the car, I start laughing as he grabs it and angrily whips it out the window again. Except he didnt, it clipped the top of his almost down window and shattered it into a thousand pieces inside his door. Now I'm laughing uncontrollably, he spends the rest of the way to my house explaining in great detail how much he hates me and wishes me dead, then we spend the next hour or so cleaning out his car. Fun times. But I never knew the window shattered so easily due to the ceramic properties of the spark plug.