What, you didn't know that?
It is a well-known fact amongst children that their art teacher often has bones in her hair. You see, when you have long locks and work with painting children you are bound to end up with paint in your hair. During the course of the day the paint will dry and become a hard stick embedded in your mane.
When you get home from work you will engage in a game of beauty parlor with your three-year-old daughter. As you take a seat in the beautician's chair for a princess updo she will exclaim, "Mama, you've got bones in your hair!"
I think this term should be added to The Funny Dictionary.
Hair Bone. n. the phenomenon of having something dry in your hair that makes it hard as a bone. Those typically afflicted include kids who eat syrup, brick layers who work with mortar, dogs who roll in the mud, and elementary art teachers.