Drilling a large coral involves advancing an open ended drill bit (about 3cm in diameter) into the coral. Below the tissue layer that is about 0.5 to 1cm thick, is dead coral skeleton. We advance the drill bit ~60-70cm, remove the bit then break out the coral core with breaker wedge, then fish the core out of the hole with a core catcher. We then start drilling again with the bit.  All the core sections need to fit together perfectly since out chronology needs to be continuous from the top of the coral.  When done drilling we plug the drill hole with either cement plugs or short disks of live tissue from the sides of the colony.