Wood-boring molluscs such as Teredo colonised the ship's decks and interior in huge numbers, eating away the wooden decking and other wooden objects such as furniture, panelling, doors and staircase banisters. When their food ran out they died, leaving behind calcareous tubes.[6] The question of the victims' bodies is one that has often troubled explorers of the wreck site. When the debris field was surveyed in Robert Ballard's 1986 expedition, pairs of shoes were observed lying next to each other on the sea bed.[111] The flesh, bones, and clothes had long since been consumed but the tannin in the shoes' leather had apparently resisted the bacteria, leaving the shoes as the only markers of where a body had once lain.[6] Ballard has suggested that skeletons may remain deep within Titanic's hull, such as in the engine rooms or third-class cabins.