Bats eat a lot of bugs — up to two-thirds of their body weight in insects daily for some species. There's an unexpected side effect of all that insect eating, though. Bat scat is described as "sparkling with insect exoskeletons." Generally the words "sparkling" and "feces" aren't found together, unless you have a toddler that's gotten into a jar of glitter.
It's a diet of insects that puts the shine in bat guano. Insects' exoskeletons, or hard outer coverings, are made of chitin. Chitin is chemically a lot like plant cellulose; it's difficult to digest, and passes through a gut relatively unchanged. If you eat a lot of shiny insects, you are going to produce Twinkle Turds.