To clean blood off a carpet, start by blotting the stain with a clean, dry white cloth to absorb as much blood as possible without rubbing, which can make the stain worse. Then spray or dab the stain with cold water (never warm or hot), continuing to blot until the blood lifts. For more stubborn stains, apply a mixture of dish soap with cold water and blot repeatedly. Other effective methods include using a paste made from salt or cornstarch and cold water, white vinegar mixed with water, or carefully applying hydrogen peroxide to break down the blood proteins. Always test any cleaning solution on a hidden area of the carpet first to avoid damage or discoloration. Let the carpet air dry or blot dry with a clean cloth after treatment.