Why would he not open that up? When my Runner had Bumble I took her to the vet for diagnosis because it didn't present itself like the bumble I had seen in my chickens no blk scab. Vet said bumble put her on antibiotics and Metacam after 7 days it really didn't look any different so I took a scalpel and made a small slit and popped the kernel out. Put antibiotic ointment on it and wrapped it she still had 7 days worth of meds to go so we finished them and her foot healed fine. If he isn't willing to open it maybe you should or put some drawing salve on it and wrap in case it opens and dirt gets into it. It may open on it's own or you could? Honest I had never used a scalpel before but sometimes you have to be your own vet.