Jinn-3(b) is a world where every eight year old gets a pony.
The pony appears the moment the child turns eight, somewhere nearby that is safe for both the pony and any nearby humans (no appearing on the freeway or inside a rickety attic). It is a real, permanent, living small horse.
For years, scientists were baffled. Culture was distorted weirdly, and industry sprung up to care for (and dispose of) ponies that were not really practical for families to own. Horses are rapidly becoming the largest portion of animal biomass on the planet. Eventually they determined that there were about two hundred "models" of pony, and through a series of experiments known as the "Birthday Surveys," researchers eventually pinned down a dramatic energy burst tied to the pony manifestations.
The inhabitants are dangerously close to discovering the Secret, and they also have a sensor network set up to detect new ponyfalls. The appearance of a conveyor will definitely set that off....