Purring first occurs in kittens that are only a few days old. It is a signal given to the mother as the kittens suckle to indicate that 'all is well'. The mother, in response, will purr back to increase the kittens sense of security and contentment.
The purr is the most significant vocal sound that a cat makes as far as humans are concerned, and we normally perceive the purr to indicate happiness and contentment. Whilst this is true, injured or fearful cats are also known to purr. These varied uses of the purr are thought to indicate in an injured or fearful cat a need for help and a way of saying 'I am helpless and no threat to you' and in the happy cat, a sense of contentment.
There are many theories on how a cat actually physically purrs. One favoured theory is that the cat contracts the larynx and the diaphragm that then produce the purr. Another theory, the 'false vocal cord', suggests that it is in fact the vibration of false vocal cords that sit behind the larynx. The third theory is that as blood passes the liver and diaphragm this causes purring in the cats chest and not through any vocal noises. This theory is called 'turbulent blood'.
Of all these theories the 'false vocal' approach is much more favoured and if you have listened to your cat and put your fingers on his throat it really does seem that the noise is ommited from the voice box area. However, the debate continues!
The reason for your cat's behaviour maybe due to an underlying medical reason. If you are concerned about your cat, always consult your vet or a cat behaviourist for professional, qualified advice.
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