It means your pup needs to the see their vet just like it would mean you should see your doctor. Parasites, bacterial or viral infection like parvo, colitis or other gastrointestinal issues, internal damage for some reason, poisoning, and a bunch of other things can be the cause. Your vet will be able to narrow things down after an exam and talking to you about what's going on. Hope your pup is felling better soon.
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