First egg-smashed

I've read that putting a golf ball in the nest will not only show them where to lay but also teach them that the "egg" is to hard to break and will stop the habit.

 

Not all that unusual, quite often the hens are surprised when an egg comes out and will investigate what it is and peck to see if it's edible, they do love fresh eggs and now and then one hen may actually start cannabalizing eggs on a regular basis if she gets away with it before you catch her.
I'd try some wooden or ceramic eggs or even golf balls as suggested above at this time in the nests, if they peck these, which they are likely do do after the hen lays then gets out of the nest, they won't learn that they can break an egg......
Also, never feed the hens eggshells in large pieces, always crush them, eggshell is a good source of calcium for the girls.

 

I've also observed that pullets are not graceful. I always have a handful of squashed eggs when the girls first start laying.