Rule Nineteen is: Remember Never to Forget Rule One. And always ask yourself: How come it was created in the first place?

When it comes to Pratchett, Rule One is Do not act incautiously when confronting little bald wrinkly smiling men.

When it comes to the Babelfish, Rule One is way simpler.
Do not mess with this fish.
She doesn't get mad and she desn't get even.
She simply forgets.