Ebay seller nes_harmonica is offering three of these old Nintendo cartridges that have been modded to contain working harmonicas. Why the heck would you do that? Turns out it’s kind of a retro in-joke for NES enthusiasts. OhGizmo’s Andrew Liszewski explains:

If you grew up in the 80′s and played video games, at one point in your childhood you had to blow on an NES cart, or inside the console itself, to get it to recognize a game. In fact I never even had an NES, but I can still remember having to do it on a friend’s system. At this point it’s almost become cliche to bring it up whenever the conversation turns to classic video games, but that didn’t stop one clever modder from attempting to turn a profit on Nintendo’s folly.

Right now Super Mario 3, Dick Tracy, and Legend of Zelda models are available. [via Geekologie]