OPEN CIRCUIT Path is broken No electricity flows
Electric current flows when a switch is in the closed, or on, position. When the switch is open, the current will not flow.
When the switch is closed, the 2 pieces of conducting material touch, which allows the electric charges to flow through the circuit. When the switch is open, the gap between the 2 pieces of conducting material prevents the electric charges from flowing through the circuit.
When the strip of metal gets too hot (too much current), it bends due to thermal expansion. This causes the switch to flip which creates an open circuit, and stops the current. It may be switched back on to allow the current to flow once again.