Unferth, the orator to Hrothgar in the epic Beowulf, is first seen mocking Beowulf's honor when trying to "call out" Beowulf as not being truly as heroic or strong as he has been made out to be. Beowulf tells Unferth that it is his drunkenness making him brave and that Unbferth does not know the entire story of the swimming challenge with Brecca.
Beowulf, that night, finds victory over Grendel (the monster who has murdered many of Hrothgar's men in the mead hall, Heorot. After defeating Grendel, the arm Beowulf took from Grendel is hung "beneath the high gabled roof" of Heorot.
It is not directly mentioned how Unferth reacts to the arm of Grendel. Instead, it is stated that many warriors and leaders gathered at Heorot to gaze upon the arm of Grendel. The story of Beowulf's victory over Grendel was known far and wide (typical of the true epic hero).
While it is not mentioned directly how Unferth reacts to seeing the arm of Grendel, one can see how his attitude towards Beowulf changes after Beowulf's victory.
Unferth gives Beowulf his ancestral sword, Hrunting, to fight Grendel's mother. Unferth knows that the sword has never failed when in the hand of a true hero. By doing so, Unferth was admitting to the fact that "he did not dare to risk his life as a loyal liegeman" and he, therefore, "fell short of glory and the honor of the court."
Unferth knows that he is not the hero that Beowulf is and the assumed wonder at the arm of Grendel (as shown by the giving of Hrunting to Beowulf) forces him to admit this.