The core looks and feels like a piece of firm gristle from a piece of meat. It needs to be removed or the boil will keep coming back in the same place. It can be removed by a doctor or apply VERY soft pressure with two cotton squares that have been soaked in Tea Tree Oil when the boil Is almost flat and finished draining. The core will usually surface and block the flow of puss and comes out of the opening. You might need to help it out with some tweezers, but it will usually make its way out.