Considering the fact that most balls I've seen tend to keep a good distance between them and their poop, I'd say it's highly unlikely that your ball ate its own poop. I do think that tttaylor's statement is pretty logical, but it really does depend on your substrate and lighting. Another possibility is that your ball might have accidentally spreaded the poop over the substrate and it dried out. I really do suggest a closer check and possibly replacing the substrate.

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