I don't know why we bother buying dog toys. Harold's favorite toys are toilet paper rolls, paintbrushes and oddly enough, clementines. While they are in season, Kurt and I can eat our way through a crate every week. I first discovered Harold's enthusiasm for them when I found him barking at a peel that had fallen on the floor. He'd toss it up in the air and roll around on the carpet batting at it like a kitten. When he gets his paws on a whole clementine, he bounces around the house like a complete maniac. We made a video of him trying to sneak one off the table.
Dogs can eat oranges in small quantities. Maybe toss your dog a clementine and see what happens? Mule doesn't give a crap about them. He just looks on, disinterested if not slightly annoyed.