Jon bought two horses, and could never remember which was which. A neighbor suggested that he cut the tail of one horse and that worked great until the other horse got his tail caught in a bush. It tore just right and looked exactly like the other horse's tail and our friend was stuck again.
The neighbor suggested Jon notch the ear of one horse. That worked fine until the other horse caught his ear on a barbed wire fence. Once again our friend couldn't tell them apart.
The neighbor suggested he measure the horses for height. When he did, he was very pleased to find that the white horse was 2 inches taller than the black.