This is a hard one to do in words. A re-occuring bumble will often be black, as opposed to brownish. If there is pus, then you will often see creamy or yellowish patches that just don't look like tissue. Also with pus, when you manipulate it, it just doesn't feel 'normal'. Sometimes it will look 'crumbly' for lack of a better word. A normal scab, over time, will start receding at the edges as new tissue fills in, a bumble will generally do the opposite, and with some of mine the edges of the skin around the bumble will actually be a little detatched from the tissue underneath rather than firm. Not sure if that makes sense in words. A scab will usually be flush, or nearly so, with the skin surface, a bumble may protrude out, or be a little sunken in. This is one that pictures would be way more helpful than words, but I don't think there are too may out there that would be good for comparison. Most pictures just show a bumble before treatment, and then a healed foot. And every wound is different depending on size and depth. You kind of learn by experience and seeing them.