What makes cats purr?

Answers:
One study determined that purring involves activation of the nerves within the voice box. These nerve signals cause vibration of the vocal cords while the diaphram serves as a piston pump, pushing air in and out of the vibrating cords, thus creating a musical hum. One veterinarians believe that purring is initiated from within the central nervous system and is a voluntary act. In other words, cats purr when they want to. Another theory is that the sound comes more from vibrating blood vessels than in the voicebox itself.

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When there happy with there owner they would purr alot and like if there just delighted or happy and when you pet them they purr somethimes

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I believe it is a vocal coard in their throught (Spelling)? As the air passes through a space that can be opened through the cord it produces a purring sound. Cats purr when they are either happy and relaxed or in pain and stressed. I read somewhere how they purr, but that was a while ago so don't take my word.

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Interesting thought but it is sure is nice to hear you know by that sound that your kitty is happy kinda of like talking i guess