Faerie foods with unusual effects. Like faerie sausages that turn the eaters into wiener dogs, faerie wines that make the drinker whiny, etc. There's a table in Palladium Fantasy RPG which has a table of ideas.
A village where everyone goes blind sometime during puberty. What could be causing this? Perhaps something in their diet. Or some malignant gene. How would an entire village where only young childen can see function?