A mechanic buys a puppy and names him Mace. As Mace grows he starts eating grass in the front yard. The mechanic never mows, so you'd think a grass eating dog would be a good thing. But, alas, the mechanic doesn't want Mace eating grass, so he keeps the dog inside.
One day, the mechanic is in his workshop beside the house, working on an engine, really straining hard. He slips and skins his knuckles. In his frustration, he throws the wrench and it lands in the tall grass in the front yard where he didn't mow. The wrench is lost. Now, this made the mechanic very sad.
A good dog knows the mood of its master. Mace knew how sad the mechanic was, so that night he escaped the house and began to graze in the front yard. He grazed all night and mowed that tall grass right down to the ground.
The next morning, the mechanic looked out the kitchen window and saw his wrench. He was so happy! He went around all day singing "A grazing Mace, How sweet the Hound that saved a Wrench for me."