What does the bard sing about inside the hall early in the narrative? Why does this anger Grendel?

My copy just has a Danish bard singing. Grendel is captivated by the music and poetry of the Geats. He hides and listens to the words and melodies, which make him, think of the beauty of life. At the same time they also remind Grendel of his isolation. Grendel is a perpetual outsider, looking for a place to belong: the music reminds him of how alone he is.