Slagworm

A cave-dwelling, caterpillar-like monster. Its mouth is large enough that it can swallow its prey whole, and the lubricant it secretes from its body allows it to slither into spaces even smaller than the width of its body. More than one has been found simply lying wait in some dark cave, mouth agape, and case after case has been recorded of cave-exploring adventurers wandering right into an open maw unawares, never to be seen again.