One of the signs that may tell you your cat may have an ear infection is the presence of a yellowish or even blackish discharge from your cat’s ears. The yellow discharge is typically pus that has accumulated for quite some time. Pus is composed of dead microorganisms, cells, tissues, and the immune system cells that attacked these microorganisms. Most vets actually consider pus as a good sign that the pet’s immune system cells are doing their job.\r