A knot is the basal portion of a branch whose structure becomes surrounded by the enlarging stem. Since branches begin with lateral buds, knots can always be traced back to the pith of the main stem.

Ah, this makes so much sense now. Excerpt from Understanding Wood at Cool Tools.

Cool Tools – How to Be Invisible

Suppose you wish to send $25,000 from Vancouver, British Columbia, to a friend in Helsinki, Finland. You would hand $25,000 cash to a Vancouver money changer (Hawaladar) in Vancouver, and receive code words (or an agreed signal such as a secret handshake) and a contact address in Helsinki. No actual cash moves out of Canada. Instead, when your friend gives the code to the correspondent hawaladar in helsinki, he will receive the equivalent in euros (less a commission) from money that is already there. To review: -There are no written documents. The exchanges are based on mutual trust (perhaps for that reason unpopular in the United States?). -Only local currencies are used. Thus, if you are sending money from the UK to Mexico, you pay in pounds and the receiver in Mexico collects in pesos. -This exchange cannot be traced because no money crosses a border.

Has this been done in a movie yet?

Cool Tools – How to Be Invisible