Short circuit

 We set up a circuit with two bulbs in it. The ammeter reading was 1.00A. Note that I'm holding a spare unconnected lead.

Then the lead was connected to the other side of the bulb. That bulb went out straight away and the current went up to 1.39A. The spare wire is called a SHORT CIRCUIT. The increased current can be dangerous because current is what heats in a circuit. The extra heat can sometimes set fire to the insulation and cause house fires.