The common belief is that cats purr to show their happiness but they also purr when frightened, severely injured, giving birth and even while dying.
Elizabeth von Muggenthaler of the Fauna Communications Research Institute in North Carolina, delved further into why a cat would waste energy purring in its last moments:
“For the purr to exist in different cat species over time, geographical isolation etc. there would likely have to be something very important (survival mechanism) about the purr. There also would have to be a very good reason for energy expenditure (in this case creation of the purr), when one is physically stressed or ill. The vibration of the cat’s diaphragm, which with the larynx, creates the purr, requires energy. If an animal is injured they would not use this energy unless it was beneficial to their survival.”
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