A spark plug shard Vs Hammer - against a car window.

[sarahs_muse]

Break a car window with a piece of ceramic.....
https://www.youtube.com/watch?v=QhlmKHbPFhU

Not breaking a car window with a hammer:
https://www.youtube.com/watch?v=XRHgJN2wjiY&feature=youtu.be&t=8s