macbth in the battle

In scene 2 the very injured Sergeant is explain to King Duncan that Scotland has repelled attacks from the Norwegians. He also hails Macbeth and, to a lesser extent, Banquo as heroes of the battle,

"For brave Macbeth--well he deserves that name--

Disdaining fortune, with his brandish'd steel,

Which smoked with bloody execution...."

He says that they found traitors Macdonwald and Thane of Cawdor.Macbeth apparently takes care of business with Macdonwald by cutting him open and sticking his head on a post, "Till he unseam'd him from the nave to the chaps,

And fix'd his head upon our battlements."