Once you're done coding and just want your CircuitPet to be "normal" again, you need to restore his base firmware.

This is quite simple, just connect your CircuitPet to the USB port of your computer and press the "Restore firmware" button on the top right.

You will be prompted with a window to choose the device you are restoring the firmware for.

Choose CircuitPet, of course.

Wait for a few seconds, and your CircuitPet will be back and running like usual.

You need to do this whenever you're done coding your CircuitPet if you want him to revert to his initial out-of-the-box functionality.