Most predatory fish feed by suction: they expand the mouth cavity rapidly, and water carrying the prey rushes in. A moray hunting inside a hole has no room for that flow, so the ordinary method fails.
Morays instead use a highly mobile second jaw apparatus. Pharyngeal jaws, present in many fish as fixed throat plates for processing food, are in morays mounted on greatly elongated muscles that can shoot them forward into the oral cavity. The forward jaws seize the prey, the pharyngeal jaws are then launched, bite down, and haul the item backward into the oesophagus. High-speed video of moray feeding published in 2007 documented the sequence directly.
The constantly gaping mouth of a resting moray is often read as threat display; it is respiration, since morays have small gill openings and pump water by opening and closing the jaws. Bites do occur, usually when a hand is placed into a crevice or when divers hand-feed, and the backward-pointing teeth make a bitten limb difficult to withdraw without further tearing. Large morays in ciguatera-prone regions are among the most dangerous reef fish to eat.