Think about what the wand is capable of, they have said that the holder of the want could conquer the universe. There is a case of surrendering or losing the wand to the forces of evil… or destroying the wand and its power so that no one can misuse that power again.

It would make sense that the first spell, taught to the next holder of the wand, would be the very spell that can destroy the wand's power. Though what I'm curious about… is why Star didnt seem to 'Know' the Wispering spell was one to destroy the wand. She said she didnt know how, but it was Toffee that pointed out "It's the first spell your mother taught you", which sounds a lot like a Tradition, passed down from wand-bearer to wand-bearer.

Unless it implies that Toffee knew Queen Butterfly personally enough to know that, or he was spying on Star even before Ludo was capable of doing so.

Sorry for the paragraph thing, I like doing a bit of analyzing now and then