Electronic trading has significantly changed the stock exchanges. Today, traders at their screens are crucial for stock trading. They can observe all transactions and bids and react to them immediately. Till Gombert examines these reactions and how they affect liquidity. Scientists around the world operate under the dogma that the supply of liquidity is manifested in the limited bids present in the order book. This perspective is expanded here. In addition to book liquidity, the liquidity supply from traders who are present at their screens, monitor the market, and can be prompted to make immediate trades through bids is also taken into account. The author empirically demonstrates both sources of liquidity for the German stock market by analyzing follow-up bids. This shows how well the market functions: significantly narrowing market spreads.