Not very spooky

In keeping with Halloween, here is my strange-not-spooky tale.  I was working late in the lab when I went down the hall to the vending machines for a Diet Coke.  I put in my change, pressed Diet Coke, and - nothing.  I muttered, and that was my last bit of change, when there was a kerlunk! from the Pepsi machine next to the Coke one, and out dropped a Diet Pepsi.  I looked around for the candid camera, or whatever, but there was no one there anywhere on that floor.  I took the Pepsi, said, "thank you" and went back to the lab.