Why can't lions and tigers purr properly?

This is my son's homework assignment. Another question is: Why will cats purr even when hurt?

Why can't lions and tigers purr properly?
It used to be believed that only the cats of the Felis genus could purr; some older texts may still say this.[3] In fact, all cats are able to purr. However, the entire Panthera genus is able to purr only while exhaling. Cats that roar lack the purring vocal cords, and use the vocal cords in charge of roaring and growling instead, making a noise similar to growling when they purr. As a result, the two sounds are often confused. The roar in these cats is a very loud growl with respect to the production method. Additionally, because these cords can only be used while exhaling, the purring equivalent sound can only be made while exhaling. Cats that are not members of the Panthera genus, even larger ones such as the cheetah, purr.[4]





According to Bruce Fogle, a veterinarian with a keen interest in animal behavior and author of The Cat's Mind, the original function of purring was to enable a kitten to tell his mother that "all is well." This often occurs during nursing. A kitten can not meow and nurse at the same time, but it can purr and nurse without any problem. The mother often purrs back, reassuring the kitten.





Other theories suggest that a cat purrs when it wants, needs, or is receiving attention, whether it be affection or medical treatment. Purring may also reduce pain, help a wounded cat to heal, or even help to keep a cat's bones strong.[1] When cats purr while also lightly clawing the ground it may mean they are trying to relieve stress or comfort themselves.





I have also read that cats purr when experiencing an extreme emotion whether it be contentment, pain, or sadness. Hope this helped. Great Question by the way.
Reply:The purring is a way to relieve stress when they are hurt.





All members of the cat family purr properly, it's just that the bigger cats (lions, tigers, etc.) sound like a deeper purr because they are larger.