Some Master Systems hid a game for players with no cartridge

A game tucked into the startup code

The Master System could run Snail Maze without a cartridge because the game was stored inside the console itself. On startup, a small program called the BIOS—the built-in code that checks the system and begins loading software—normally looks for a cartridge. With no cartridge inserted, holding buttons 1 and 2 during startup triggers a different path: the BIOS launches the maze instead.

That makes the game more than a hidden menu option. Its maze graphics and rules had to fit in the console’s own startup memory, rather than arrive on a separate game cartridge. The result is deliberately simple: steer a snail through a maze toward its exit, using the Master System’s basic controls.

A small detour in the boot process

The secret depends on timing. The buttons must be held as the console powers on, while its startup code is checking what to do. Press them after the system has already moved on, and the opportunity has passed. The console’s ordinary job—starting a game from a cartridge—therefore doubles as the doorway to the built-in one.

Because Snail Maze lives in the system rather than on a game card, it also reveals an unusual use for startup code: a few spare moments before a cartridge game begins could become playable content. No new game was needed; the console already had one waiting inside.