* No central registry: There's no official list or database that tracks every single tongue twister ever created.
* Constantly evolving: New tongue twisters are constantly being invented, and some older ones fade from use.
* Regional variations: Tongue twisters are often specific to certain languages, regions, or cultures.
* Subjective definition: What counts as a tongue twister can be a bit subjective.
However, you can find many lists and collections of tongue twisters online and in books. These collections can give you a sense of the variety and popularity of different tongue twisters.