Why does PUNCHING Sonic 3D trigger a Secret Level Select?

I explain why hitting your Sonic 3D cartridge brings up a secret level select screen in this episode of Coding Secrets.

Is That You or Are You You by Chris Zabriskie is licensed under a Creative Commons Attribution license (https://creativecommons.org/licenses/by/4.0/)
Source: http://chriszabriskie.com/reappear/
Artist: http://chriszabriskie.com/