This "greenish slug" could be an abscess or hematoma. Abscesses are caused by an infection of the ear and usually occur after a fight or some other ear injury, or after an irritative process such as scratching the ear. Abscessas are found below the ear and Hematomas involve the flap. A Hematoma is a blood clot under the skin. It can also be caused by trauma or by violent head-shaking or scratching at the ear. If either of these two things exist, a vet should be consulted.