why do chickens rub their beaks in the dirt?

[JD4570]

Mine use limestone bricks I left around the coop for them. I also have to remember not to wear any open toes shoes around them.

 

[jpfenimore]

I recently watched a British documentary about chickens that suggested that they do this to get attention. Any opinions on that? I'm curious because I have observed what seems to be my girls trying to teach our "dumb blonde" Lucy to do various things (like jump up on the roost) and they often appear to scratch their beaks in front of her as if to say "watch this!"
Thanks,