Big cats are very interesting, even though your black cat may resemble a panther, it definitely can’t roar like one. There are obvious factors as to why a 10 pound cat is never going to sound like a 200 pound lion, but putting size to the side there are other biological reason that prevent cat’s from roaring, and lions from purring.
The people from Big Cat Rescue made the video on the tab above where they go into detail as to why large cats can’t purr and small cats can’t roar. It has to do with a bone in their chest area. Large cats have a soft bone that vibrates and makes the “roaring” sound, cats in the other hand have a small solid bone that does not vibrate as strong.
Some people claim that large cats like Lions, Tigers, and Leopards can purr, but only when they exhale – which is not a real purr. According to them, a real purr is a requires continuous inhale and exhale. Even if they could, I think I would confuse the purring with a roar and stay away from them after that… [Big Cat Rescue via io9]