Why do cats have scratchy tongues? In this Deep Look video, the channel goes deep (ahem) on the functions of cat tongues. The video is presented in Ultra HD, and we get lots of ultra-closeup slow-motion cat material.
Getting back to the core question, there are lots of reasons. First, cats use their tongues to groom their coats. Their tongues have "papillae" that operate as grooming brushes, doing an effective job of removing surplus hair. Cats want to be super-clean because they are ambush predators—an errant whiff of cat scent might tip off their prey. Plus, as illustrated in the video below, the structure of a cat's mouth and tongue make lapping up liquids a rather complex process.
Make this fullscreen and learn all about cat tongues:
If video isn't your thing, or you're curious about the making of this video, check out KQED's blog post. If you just love watching animals drinking, dig this video roundup of animals drinking in slow motion.