Chapter 6, Page 84, In the following speech Grendel sarcastically mocks Unferth. "I've never seen a live hero before. I thought they were only in poetry. Ah, ah, it must be a terrible burden, though, being a hero- glory, reaper, harvester of monsters! Everybody always watching you, weighing you, seeing if you're still heroic. You know how it is- he he! Sooner or later the harvest virgin will make her mistake in the haystack." What is Grendel referring to when he talks about the harvest virgin?
An old tradition where during the harvest a virgin is sacrificed to ensure good crops. He is saying she might make a mistake, the way Unferth may make a mistake and do something unheroic, like killing his brother.