You pick up a ring in the bargain bin and take a look at it. The vintage packaging, faded from years of sitting unused, looks like it might be from a 50s joke shop. The ring inside looks like it's made of cheap plastic, and there is a small chip in the stone set into it. Looking a little closer, you can see some information on the packaging:
INCREDIBLE SWAP RING
Impress your friends with the incredible swap ring! Once a day, this ring will allow you and another person to make a magical trade. Switch any features or attributes; shock your friends by trading height, eye color, or anything else you'd like! Just pick a person, an attribute, kiss the ring and... ALAKAZAM!
You have your doubts, but the sale sticker on the package says it's only a few dollars. You bring it up to the front and ask the clerk why it's in the bargain bin if it really works. They respond that it was returned because it will swap one extra attribute with the chosen person at random. You give them a skeptical look; half because you can't believe they are serious about this magic stuff, and half because you're embarassed for bringing it up in the first place. You want to get out of the store, and for some unknown reason, you hand the clerk some money and buy the ring on your way out. You throw away the packaging as soon as you get outside and slide the ring into your pocket. You don't want everyone you pass on your way home to think you're a total lunatic.
As you make your way home and sit down on your bed, you take the ring out of your pocket. You feel pretty silly. Still, you might as well try it once before you throw the thing out. Putting it on, you think of who to swap with...