Question

When Grendel speaks of Unferth and says, "I could crush him like a fly" (89),what literary device is being used?

Answer 1

I'd say two literary devices are used in this line.
1. simile: using  the words like and as to compare something
2. hyperbole: exaggerating things - he couldn't really crush him like a fly, but he could hurt him or kill him nevertheless