There are a few reasons why this might be a common belief:
* Muscle relaxation: As a dog nears death, their muscles may relax, including the muscles in their tongue. This can lead to their tongue appearing to be hanging out, but it's not a sign that they are dying.
* Breathing difficulties: Dogs that are struggling to breathe might have their tongue out due to labored breathing. However, this is a symptom of a medical condition and not a sign of impending death.
* Post-mortem stiffness: After a dog dies, their muscles stiffen, which can also make it look like their tongue is hanging out.
If you see your dog with their tongue out, it's important to observe their other behavior:
* Are they breathing normally?
* Are they responsive?
* Do they seem lethargic or in pain?
If you have any concerns about your dog's health, it's always best to contact your veterinarian immediately. They can assess your dog's condition and determine if there is any reason for concern.