A rich man in a certain town once owned a dog and a cat, both of which were very useful to him. The dog had served his master for many years and had become so old that he had lost his teeth and was unable to fight any more, but he was a good guide and companion to the cat who was strong and cunning.
The master had a daughter who was attending school at a convent some distance from home, and very often he sent the dog and the cat with presents to the girl.
One day he called the faithful animals and bade them carry a magic ring to his daughter.
“You are strong and brave,” he said to the cat “You may carry the ring, but you must be careful not to drop it”
And to the dog he said: “You must accompany the cat to guide her and keep her from harm.”
They promised to do their best, and started out. All went well until they came to a river. As there was neither bridge nor boat, there was no way to cross but to swim.
“Let me take the magic ring,” said the dog as they were about to plunge into the water.
“Oh, no,” replied the cat, “the master gave it to me to carry.”
“But you cannot swim well,” argued the dog. “I am strong and can take good care of it.”
But the cat refused to give up the ring until finally the dog threatened to kill her, and then she reluctantly gave it to him.
The river was wide and the water so swift that they grew very tired, and just before they reached the opposite bank the dog dropped the ring. They searched carefully, but could not find it anywhere, and after a while they turned back to tell their master of the sad loss. Just before reaching the house, however, the dog was so overcome with fear that he turned and ran away and never was seen again.
The cat went on alone, and when the master saw her coming he called out to know why she had returned so soon and what had become of her companion. The poor cat was frightened, but as well as she could she explained how the ring had been lost and how the dog had run away.
On hearing her story the master was very angry, and commanded that all his people should search for the dog, and that it should be punished by having its tail cut off.
He also ordered that all the dogs in the world should join in the search, and ever since when one dog meets another he says: “Are you the old dog that lost the magic ring? If so, your tail must be cut off.” Then immediately each shows his teeth and wags his tail to prove that he is not the guilty one.
Since then, too, cats have been afraid of water and will not swim across a river if they can avoid it.
Why Dogs Wag their Tails – Philippine Folk Tales