Getting a game through a publisher's certification process can be difficult. Games are tested in extreme conditions and fail for the slightest error. In the '90s, one developer snuck their games through Sega's certification with a few clever tricks that disguised glitches as part of the game.
Traveller's Tale founder Jon Burton describes his secrets in a new video (h/t Polygon) that explains the various ways he disguised glitches as random secrets. Sega's certification process was notoriously stringent, failing developers if their games crashed for any reason. To get through this, Burton had glitches and crashes lead testers to fake bonus levels and select screens.
The process was devious but easy. Instead of having the game present specific error messages when it crashed, he would program his games to perform a certain task instead. In 1994's Mickey Mania, instead of showing an error message, Burton programmed the game to throw testers to random levels while claiming they encountered a hidden "time warp". He repeated the process the following year for the Genesis' version of Toy Story. This time, errors sent testers to bonus levels.
Burton's most drastic fix was on 1996's Sonic 3D Blast. In order to disguise crashes as legitimate gameplay features, he made it so any error would redirect to a level select screen and congratulate players on finding the secret. This was never removed after testing, which means it's possible to access the game's level select simply by hitting the cart or system hard enough. When the cart disconnects from the machine, it triggers the level select.
All of these tricks are smart and fun ways of sliding through a process that was incredibly punishing. Plus, now we know that you can select any level in Sonic 3D Blast if you smack your console like the Fonz.