Fatty Knees And How To Rig What Is This Soft Fatty Lump On The Back Of My Dog's Knee?

What is this soft fatty lump on the back of my dog's knee? - fatty knees and how to rig

I know the other day that my dog has a soft, fairly large mass behind the knee. I thought I had something of a mistake and it was an infection, but does not bite or hole of any kind, we believe that it was inflated, the pressure to experience again, but only a little bleeding. What is it? appears to be in pain at all, and it seems that bothers you somewhere. IM is still concerned Tho.