Peanuts?

So here I sit in front of the computer eating some pistachios. My eye glances down to the can. I see the ingredients list: Pistachios, Salt. Then, right below it, I see the strangest thing ever. Three little words: "MAY CONTAIN PEANUTS". What? How does THAT happen? I'm fairly certain that peanuts and pistachios are pretty different. One comes from trees, the other from bushes. Don't believe me? Grab a can of shelled pistachios from Inter-American Products, Inc. of Cincinnati Ohio. Very strange, but that's pretty much par for my life.