How does a spring pop up the toast?

Push the lever down to start.

1. Push the lever down. The spring stretches. A latch holds it down.
2. The wires inside get hot.
3. A metal strip warms up and bends. It lets go of the latch.
4. The spring pulls back. Up pops the toast!

The bread, the glow and the toasting time are added by this page. A higher number makes browner toast. Only a grown-up uses a real toaster.

Watch the lever. What makes it come back up?