Traders bid on the floor (trading pool). They accept trading instructions from customers (investors) or place their own orders for trading, but investors cannot enter the market directly. Therefore, off-exchange investors can only contact on-exchange traders by telephone or order form, while larger customers have direct telephone contact with their traders, and ordinary customers only have handwritten orders.
Those who give orders inside and outside the venue are called "runners". They pass the orders of customers in different places to traders, and then return the receipt recording the transaction results to customers in different places after the transaction is completed. The pieces of paper in the hands of traders on the floor are the order forms and telephone order records that come in from outside the floor. When a trading order is executed (or cancelled), the order in hand is useless, so it is thrown away because it is impossible to hold a large number of orders in hand.
When traders are excited about their trading results (such as large profits), they often throw notes to express their feelings, just like people throwing hats in the air when cheering, which is also allowed.