****** a piercing scream assaulted lucas ears as they plummeted towards the bottom of the large ravine , branches and leaves whipping them from all sides until at last they were abruptly halted half way down by a large soft bank of moss that tipped them rolling and sliding into a large open tunnel that continued rushing ever downwards as a torrent of water and mud lapped at their bodies swirling them round and round like leaves in a storm drain .