"Human." Twilight deadpanned to the farmer standing beside her in the human world, "What is that horse doing?"
"Why, ol' Clacker there's just takin' a lick of the salt lick."
"What, ya got somethin' against that? It's for their health, y'know."
"What are they made out of?"
"Salt and other essential nutrients for the horses. Why?"
"Um..." Twilight began, "Gotta go!"
Twilight proceeded to become a multi-millionaire in Equestria's healthcare industry.
Because Salt Lick blocks.
And salty lollypops.
And technically it was Rarity that did the marketing. Twilight brought the idea.
Surprisingly, Rarity reacted rather well to the idea of licking a block of minerals on a stick.