an abscess. we have a mixed breed too, pitt, rott, boxer, and lab mix. she had exactly what you discribed. its common. can start from a simple misquito or flea bite or even a little bitty nic on his skin. its about $800 to remove. it doesnt hurt at first but the abscess will get bigger inside. they can get the size of a grapefruit underneath the skin. then it will hurt and cause problems (possibly) on top its just a big pimple looking thing. at first, nothing comes out, over a few months to a year. it will start seeping pus everywhere. if its really small tho, like you caught it early, you can get him antibiotics that could make it go away. the only way to know if its small enough is to have a vet see him. by the way, if your dogs like mine, it doesnt look like it hurts but this mix of breeds seems to tolerate it more than others but it will hurt eventually. antibiotics can range from $30-$70. i hope this helped. oh and it wouldnt seem like it hurts if you just squeeze the bump. the bump is dead skin and the nerves are dead too. its on the inside that it hurts. if you pinch around it about an inch of skin. does the dog like his lips and look back or does the fur on his back cringe? then it hurts.