Kissing was invented in the city of Thusk, a seaport with thousands of citizens, yet only one dentist. Her services were scarcely needed, for the civic biologists had rendered most of her profession obsolete.
A solitary starfish the size of a penny lived inside each resident's mouth, which it treated like a wandering aquarium. Every few hours, it would scurry out from its nest beneath their tongue and repeat the process of cleaning. One by one, it draped itself around their teeth, reinforcing their alignment and devouring every particle of filth.
This resulted in a cultural contradiction; while all who dwelled within Thusk had perfect, ivory teeth, it was considered obscene for them to smile, lest they expose their inner echinoderms. Even so, in the privacy of their own bedrooms, lovers would allow their bare lips to touch, and sometimes even exchange starfish with their tongues.
Local prostitutes taught this art to visiting sailors, who exported it to all the world's harbors thereafter. Even without starfish of their own to reveal, they found that the intimacy remained.
There are other uses for keeping starfish in one's mouth.
The priests of Thusk believed that perfect teeth could bring immortality.