Grendel is your classic "outcast." Night after night he hears the Danes loudly celebrating in Herot (the mead hall) and it drives him mad with rage and envy. So at the root of his attacks are the very human emotions of sadness, isolation and envy.
Old English language
Old English (Ænglisc, Anglisc, Englisc) or Anglo-Saxon is an early form of the English language that was spoken and written by the Anglo-Saxons and their descendants in parts of what are now England and southern and eastern Scotland between at least the mid-5th century and the mid-12th century. What survives through writing represents primarily the literary register of Anglo-Saxon.
It is a West Germanic language closely related to Old Frisian and Old Saxon. Old English had a grammar similar in many ways to Classical Latin. In most respects, including its grammar, it was much closer to modern German and Icelandic than to modern English. It was fully inflected with five grammatical cases (nominative, accusative, genitive, dative, and instrumental), three grammatical numbers (singular, plural, and dual) and three grammatical genders (masculine, feminine, and neuter). The dual forms occurred in the first and second persons only and referred to groups of two.
In ancient Scandinavia and Germanic Europe a mead hall or feasting hall was initially simply a large building with a single room. From the fifth century to early medieval times such a building was the residence of a lord and his retainers. The mead hall was generally the great hall of the king. As such, it was likely to be the safest place in the kingdom.
The old name of such halls may have been sal/salr and thus be present in old place names such as "Uppsala". The meaning has been preserved in German Saal, Romanian Sala, Dutch zaal, Icelandic salur, Swedish sal, Finnish sali and French salle (all meaning "hall" or "large room"). In Old English, sele and sæl were used.
English folklore is the folk tradition which has developed in England over a number of centuries. Some stories can be traced back to their roots, while the origin of others is uncertain or disputed. England abounds with folklore, in all forms, from such obvious manifestations as the traditional Robin Hood tales, the Brythonic-inspired Arthurian legend, to contemporary urban legends and facets of cryptozoology such as the Beast of Bodmin Moor.
Morris dance and related practices such as the Abbots Bromley Horn Dance preserve old English folk traditions, as do Mummers Plays. Pub names may preserve folk traditions.