I was out for dinner with a couple of friends and just when we were about to enter our cars after dinner, I saw what I at first thought to be Mars due West at roughly 30-40 degrees elevation (seconds later I realized Mars rises in the East these days). Then I saw it moving slowly and exclaimed happily "Look! It's the ISS!" and we all watched it for about 10 seconds and I was preparing to give a short speech about some random fact I know about the ISS. Now, as a budding amateur astronomer, I've been a regular user of the Heavens Above Android app (until it stopped updating 3 weeks ago) and have seen tens if not hundreds of ISS flyovers and Iridium flashes, so I was 100% certain it was the ISS we were seeing.

Just at that moment, the thing went almost entirely dark (quite like an Iridum flash does when it ends) and started flashing intermittently right thereafter. It continued on its previous course, but now looked like a regular high-altitude aircraft; I watched it for about 20 more seconds before getting in the car with my thoughts ascramble. My first half-drunken thought was "this must have been one of those refueling aircraft that have five bright lights on the underbelly that I read about just yesterday" but now I'm not so sure.

If any of you can check for known past satellite flyovers and similar phenomena, this happened at 11:36 PM CET at 46.5N, 15.6E. Other than that, I might have to settle for never knowing for sure.