Beheadings:  The toppling of heads begins when Beowulf's mother beheads the warrior Aeshere.  Later, Beowulf will behead Grendel after defeating him in the Great Hall, Heorot, where the monster's arm and claw are later displayed from the rafters.  Not content with Grendel alone, later, Beowulf brags,  "I beheaded Grendel's mother in the hall / with a mighty sword" (2139-2140). *Note:  Haney Translation. 

Fratricide:   According to Johnathan A. Glenn of the University of Central Arkansas:  "the issue of fratricide plays a significant role throughout Beowulf: See lines 81b-85 and 1162b-65a (foreboding of future problems in the kingdom of the Danes); 584-94 and 1165b-69a (Hunferth) and 1455-64 and 1519b-28 (Hrunting, Hunferth's sword); 902b-04a and 1709b-22 (Heremod); 2435-67 (Hrethel and his sons; the "Elegy of the Old Father"); 2741-43a (Beowulf's claim of innocence)."