Complex sentence: Grendel, a troll-like monster said to be descended from the biblical Cain, is pained by the sounds of a joy he cannot share, attacks the hall, and kills and devours many of Hrothgar's warriors while they sleep.
Split into simpler sentences: Grendel, a troll-like monster said to be descended from the biblical Cain, is pained by the sounds of a joy he cannot share. Grendel attacks the hall, and kills and devours many of Hrothgar's warriors while they sleep.