The '' Sonic & Knuckles '' cartridge features '' lock - on '' technology that allows it to be physically attached to the '' Sonic 3 '' cartridge , creating a combined game , '' Sonic 3 & Knuckles '' .
The '' Sonic & Knuckles '' cartridge features a '' lock - on '' adapter that allows it to be physically attached to other Genesis cartridges . 
 Connecting the '' Sonic 3 '' cartridge creates a combined game , '' Sonic 3 & Knuckles '' .