Reasons for a small amount of blood in cat vomit:

1. Gastroenteritis or digestive problems: This is one of the most common causes of cat vomiting. It may be due to dietary allergies, improper food, Caused by gastrointestinal infections, indigestion and other problems. If the vomiting caused by gastroenteritis is severe, it may be bloody.

2. Stomach irritation: Cats may swallow things they should not swallow, such as hair, grass, plastic, etc. These substances will irritate the stomach wall, cause vomiting, and may be bloody.

3. Liver disease or kidney disease: These diseases can cause the accumulation of toxins in the body, causing vomiting, which may be bloody.

4. Tumor: Tumors in the digestive system of cats may also cause vomiting with bloodshot eyes.

5. Infection or parasites: If the cat is infected with viruses or bacteria, or has intestinal parasites, it may also cause vomiting with bloodshot eyes.

6. It may be caused by hair ball syndrome. The vomited stuff contained a small amount of blood. Give cats hair removal cream, etc.