Hard to say from the photo, but there may be something in there that shouldn't be, maybe fluid or infection and yolk. What you can do, if you want, is try a round of antibiotics, but it can't be something useless like Terramycin. It would have to be penicillin injections, which are easier than you think. Most feed stores carry penicillin procaine in bottles in their fridge and the syringes and needles. I use a 22 gauge needle, though sometimes it's easier to get the pen through a 20 gauge (bigger reaction from the bird because the needle is larger, though). You give 1/2 cc in the breast muscle normally, but for this, I give 3/4 cc-1cc since it's hard to fix, and do it for 3-4 days in a row. Then, you hope it kicks out any infection. It's really a shot in the dark and may not fix the problem other than temporarily. It did keep one of my hens going for a year, by treating each recurrence, but the last time, it didn't work and she eventually died.