knocking, n.All

Before alarm clocks, a professional ‘knocker up’ was hired to tap on windows or bang on doors

Knocking is a much lighter way of punching someone's house untill they come out and stop you.

Knocking is a slow but sure way of putting the skids under your prospects. Push in the door softly, and all things are yours—knock and nothing shall be opened unto you.

Knocking is the polite thing to do — Whistle before you walk into a stranger's camp.