A tail-kinker was a type of plant-derived spice from Sivao. They grew on trees. It was found in the shape of a ball, and was extremely hot when ingested as food, and often used in practical jokes.
The oil of the tail-kinker was used to help wake up Brightspot to-Srallansre during Walk, after being tossed into the river by Tail-Kinker to-Ennien
Some of the Sivaoan like to chew on them
((TOS novel: Uhura's Song)