infections basically. In addition to lymphedema (build up of fluids, mostly lymph, in the legs), it also has cellulitis which is an infection in the skin, and boils. It's inevitable from poor hygiene coupled with lack of movement. Our lymphatic system is designed to work with movement to help push lymph around our body.  The infections are not helped by constant exposure to feces and urine, and the cracking and skin sloughing that happens in advanced stages of lymphedema.  Another factor on why his legs look like they are rotting, is in addition to everything above, he also has diabetic neuropathy at play. There are also likely a handful of other obesity related conditions (high blood pressure aka hypertension, high blood sugar levels, and a host of hormone imbalances) that all contribute in their own way. If anything this is an interesting case study in how the human body breaks down from excessive over eating and lack of movement.