What's up with the dirty treats?

KD had a rawhide that she had taken outside the other day and it was softer today. She ran around with it and chewed on it for a while and then she buried it in a hole that the other dogs had dug in front of the pond. Later in the evening, she dug up the now dirt covered rawhide and was running around with it and then was laying down to eat it. She gave it to me in the house and I washed it clean and gave it back. I don't understand the eating of dirt, but I guess we have moved a long way away from the animal state that dogs still live in and if we humanize them, we are wrong.