Terriers must think tennis balls were made just for them! Well, their hair does resemble one!! I had an Airedale, Paddel, who collected them. We lived behind a country club court-had to put all of the balls(372) in garbage cans and he would tip over the cans and "count" them- kept him busy for hours-he seemed to know when one really smelly, disgusting one was thrown away-he would go to the real garbage cans and howl until someone got the prized possession out!!