Have you ever been licked by a cat? Did you notice that they have a very rough tongue? It kind of feels like you are being rubbed with sandpaper. Right?
A cat's tongue is covered by little hooked projections called papillae. They are hair-like in nature and point towards the back of the mouth and they cover the entire tongue.
The purpose of these papillae are to aid the cat when it grooms itself. Because a cat's fur is really soft and fluffy, a regular tongue would only spread saliva over the fur causing matting. These papillae act like a brush. They smooth out the fur and remove tangles and loose hair.
They may even aid the cat when it eats. Helping to push food towards the back of the mouth and then finally down the throat.
So, now if someone asks you why cats have a rough tongue, you can give them the answer.