This page details bugs of Galaga (Arcade).
Crashing the Demo
During the demo, the Fire button is active for a brief moment while the player ship is being abducted by a Boss Galaga. If you manage to destroy the enemy before the abduction is complete, you'll regain full control of the ship. This usually leads to the game crashing and triggering the watchdog timer, which reboots the hardware.
An in-depth explanation of the bug and the responsible code can be found here.