It is a unique vocal feature shared by small-breed cats such as the domestic cat, bobcats, cheetahs, lynx and pumas. Purr is  unique from other vocal noises in that it is produced during the entire respiratory cycle (both inhaling and exhaling). Many behaviorists believe that the original function of purring was to enable a kitten to tell its mother “all is well”. This conversation often occurs during nursing and, since a kitten can’t meow (vocalization during exhaling) while nursing, purring became a universal signal of contentment between mother and kitten.

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