Obsessive Licking... does anyone know why?

[Tegan]

In the last couple of weeks Kali has been obsessively licking a few things in our house. She has been licking one of the stones that make up our fireplace surround, the door to Gypsy's crate (a dog we're dogsitting), my spinning wheel, and the refrigerator door. If it was just the fridge I would assume there was just some food residue, but she seems to lick the rock the most. I try to stop her when I see her licking things but I'd really like to know why she's doing it. She gets lots of exercise (two walks a day, one short on leash and a long off leash usually about an hour and a half) and has lots of toys so I don't think it's because she's bored. Does anyone have any idea of why she's licking things?

[Yvonne, Riley, Murphy and Luca]

Are all the items cool to the touch? Or possibly the rock could taste salty to her? I am not sure you want to try licking it to find out, but it is a thought.

Riley licks the refrigerator door, but I thought he just did it because it is stainless steel and then he can watch me clean it again :)