In Act 4, Scene 2, Lady McDuff has just had a talk with her cousin Ross. She is upset and angry. She then turns to her son and argues with him about his fathers innocence
Sirrah, your father's dead. And what will you do now? How will you live?
As birds do, Mother.
Lady MacDuff continues to argue with Sirrah about his father.
With what I get, I mean, and so do they.
What, with worms and flies?
The argue and play on words continues.
Poor bird! Thou'dst never fear the net nor lime, the pitfall nor the gin.
Why should I, mother? Poor birds they are not set for. My father is not dead , for all your saying.
And on it merrily continues.
Yes, he is dead. How wilt thou do for a father ?
Nay, how will you do for a husband?
They are now insulting each other with big words, while still fighting.
Then you'll buy' em to sell again.
Why, I can buy me twenty at any market.
In the next part of this scene, a messenger comes to tell Lady MacDuff from her impending doom.
Bless you, fair dame! I am not to you known, though in your state of honor I am perfect. I doubt some danger does approach you nearly. If you will take a homely man's advice, be not here found. Hence with your little ones. To fright you thus methinks I am to savage; To do worse to you were fell cruelty, which is too nigh your person. Heaven preserve you! I dare abide no longer.