David Mamet's Three Uses of the Knife

Mamet's idea is based on how an object can become a metaphor and embody the change that occurs between characters during the story...
You use your knife to go out and cut down food for your lover, you come home and you use your knife to shave to look good for your lover and then you use your knife to cut out her lying heart when you find your lover cheating on you.
- Screenwrtiers' Masterclass (Kevin Conroy Scott)