This is the second time we've had a female squirrel come to us with some substance on its face and paws that is blackish. We are wondering if this is sap from gnawing at a branch of a tree that is sap-creating. Perhaps the female is nest-building? Most conifers create a thick sap that is difficult to remove so we've been speculating that perhaps this is a sap that has gathered dirt to it given how sticky it can be. Has anyone seen these black faces and paws and fur before? I've included a picture. Thank you for any help.