Given that you posted this a while ago, I'm going to assume you're just seeking general rather than specific information. One possible indicator of blood loss is that the dog's gums will appear pale pink to white. One way to test this is to gently but firmly press your index finger over the base of an upper canine tooth--i.e. "fang"--and then withdraw it. Normally that area will appear pale when you remove your finger but then become pinker. If it stays pale to white, the animal has serous problems and should be checked by a veterinarian immediately.
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