The pet has a small swelling or soft lesions with or without a foul-smelling discharge. Lumps in pets can be quite disturbing; however, they are not all causes for alarm. Lumps can come in a variety of sizes, and while some can be hard, others may be very soft. Furthermore, while some lumps can be painful to dogs and cats, others are not. Common types of lumps in dogs and cats include lipomas, sebaceous cysts, hematomas, warts, infected hair follicles, abscesses and various types of tumors/cancer.