Answer:
It was shown when Grendel's mother came to avenge his death in the hands of Beowulf.
Step-by-step explanation:
To avenge means to cause a person harm because they did the person something bad. In the poem Beowulf, Grendel was characterized as a monster who threatened the kingdom of Hrothgar, who was King of the Scyldings in Denmark. He terrorized the King and his subjects.
When Beowulf who was from the Kingdom of the Geats heard of this he took pity on the Scyldings. He came to their kingdom and challenged Grendel. He later caused the death of Grendel. Grendel's mother was infuriated at this and came to avenge his death. She did not succeed for Beowulf also defeated her.