Why is a cat's tongue so rough?

Have you ever wondered why a cat's tongue feels so rough? Check out this close up shot.

A cat's tongue is covered in backwards facing spines, about 500 microns long. These are called papillae and they contain keratin (the same stuff your fingernails and hair is made of) making them quite rigid. These are used in grooming and act almost like a hairbrush.

I won't show you a photo of this, but a cat's tongue isn't the only body part to have spines. The penis has a band of about 120–150 backwards-pointing penile spines, which are about one millimeter long. These rake the inside of the females vagina, triggering ovulation.
So there you go. Now you know why a cat's tongue feels like sandpaper, and why female cats make such a loud noise when mating!