I would be tempted to give the chicken 1/2 of a 25 mg Benadryl tablet orally in the back of the throat or crushed into food one time to see if it causes swelling to go down. Several people over the last few years have had tick bites which have caused bluish swelling of a wattle. I don't anything that looks like a tick bit, but it won't hurt. Let us know if it helps. I would check with a vet if this doesn't change. An abscess, wound, tumor, hemangioma are all possibilities. Tumors tend to be firm. Pus inside an abscess can be soft and then firm up into cheese-like consistancy.