I decided to try another way of removing a knot, which I saw on Youtube.



The idea is to put the brush up tight to the vise jaws, and crush the glue bulge above the knot. It looked good on the video, but for me the vise kept slipping off the glue bulge and just crushing hairs. I tried to push the knot into the vise as I cranked down on the jaws, but all I accomplished was to cause the brush to come apart.



I trimmed the hair and sussed out my options. I assume a bit of epoxy will put the handle back together. But it was actually good that it happened, because now I can get to both sides of the knot, plus really be able to see what's going on during knot removal.
I started with a 1/8" bit and drilled a few holes.



You can see my progress from the back side.