What does Judges 4:21 mean?

But while Sisera was exhausted and asleep, Jael, Heber's wife, quietly took a tent peg and a hammer, crept up to him, and drove the peg through his temple into the ground. He died instantly. Judges 4:21 - Modern Text Bible

(Jael takes bold, violent action. She kills Sisera while he sleeps, ending the threat he posed.)