Greta is a great dog. That is the consensus of the staff and volunteers at the Animal Shelter of Martha’s Vineyard. She is a medium-sized bundle of love with a grizzled but soft coat, a tail that starts thumping when you speak to her, and big brown eyes. Her intelligence shows in her expression and in her eagerness to please She is crazy about people, including the small ones, is indifferent to cats, and would prefer to be the only dog in the household.