How would the dog ask people to look for his owner? How would he do it if he can't talk like people?

A lost dog can ask people to look for his owner by using any of these approaches.

Explanation:

A lost can that has lost his owner will never feel comfortable, the dog will become restless and approach people form different angles, the dog will keep back and keep pointing to his neck tag. This neck tag will give the one who wants to help a clue on who the owner could be and so this helper would help contact the owner or report  to the appropriate authorities.

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