Odd dog

Here is Chloe doing one of the things I rather wish she wouldn't. Unlike her other 'bad habits' (Natural spaniel behaviour, she says) this is one I can't understand.
She is digging up a stone which she appears to have selected carefully and then takes away in a very purposeful manner. If the car is near she will return to the car with it so that we actually have a number of her stones parked in the back of the car. Do any bippers have any suggestions? I'd be really pleased to know that this is not to do with previous puppies which she is mourning or future ones she would like (she'd be out of luck there as we had her 'done'!)