The knowledge gained through the trials Beowulf faces, during his battles with Grendel and the "She Wolf", are wide and many. These include Grendel's ability to dull any blade edge the comes in contact with him and that Grendel's mother's blood will melt through numerous materials in a mater of minutes. Beowulf also learns that his great and powerfully crushing strength, given to him by God himself, is his only weapon of choice against his enemies.
When Beowulf and his crew of Geat warriors first arrived in King Hrothgar's domain they learned in further depth the damage Grendel had caused. During the beginnings of Beowulf's death match with the famed Grendel, Beowulf attempted to use his great sword to slaughter his foe, only to soon find out the no blade can Pierce Grendel's thick hide. After becoming aware of this Beowulf began to use grapple techniques and triumphed shortly after ripping his enemy's limb off.
Later Beowulf is celebrated as a great hero and hired for a new mission. He was to slay Grendel's mother, the greatly feared "She Wolf". After claiming a decorative sword, made for a giant, from the "She Wolf's" lair he thrust it into her, covering the weapon in her blood. As Beowulf makes his accent he discovers his massive sword had been reduced to merely a jewel encrusted hilt.