Laughing heartily, the winning dog was cheered and whistled at by the crowd. So, who was laughing heartily? We would have to say that the dog is the dangling modifier because we know that a dog cannot laugh, and we don't know who is laughing. So, in this case, we can say that the dog is laughing to fix it.
As he laughed heartily, the winning dog was cheered and was whistled at by the crowd.