The whole CD doesn't shatter, but the edges of the break do. To see this effect on steroids, put a CD through a shredder: a common security procedure. You're playing Russian Roulette with your eyeballs if you don't wear eye protection when doing this.
I personally broke many CDs, it's kinda hard to do but when they snap small bits from broken edges fly off everywhere. I even saw CD that broke inside of drive. Granted it was put in with a crack in the middle but still it broke. Maybe it's just my feeling but I think that CDs back in the days was made out of a bit less flexible, ticker and more brittle plastic. Those produced today I can bend in half and they don't snap as easily as 20 years ago
