Me, but only if you tell me how you did your trick...
It looked like a white balloon floating on air currents. Or maybe an interior reflection on exterior glass. How did you do it, if I may ask?
Deetee and CLD,
Thanks for your interest, I'll be glad to explain how I did the trick. But first, I must give credit to someone on the internet, whose name escapes me at the moment, for the idea.
Basically the UFO is a reflection of a light on a window glass, as CLD correctly guessed. But there are many details and subtleties to the trick, because the idea, of course, is to leave a strong impression that it is an object floating in the sky far away from the camera.
Basic materials I used:
- A flashlight
- A piece of aluminium foil
- A piece of cardboard
- An analog video camera (why "analog", I'll discuss later)
- A wired external mic for the camera.
First, I prepared the flaslight by covering the screen with a piece of aluminium foil, leaving only a 5 mm diameter hole in the center, so as the light looked circular and concentrated in a small dot. I also masked the light with several layers of yellow colored plastic (the one used to wrap candies) to reduce the light intensity and to minimize reflection beams on the glass.
All the action took place in a closed room on a 17th floor. To create the auditive illussion that the UFO is floating in the air I used the external mic to capture various outside noises; I simply left it hanging down from the windowsill with the window closed.
The most "revealing" part of the trick, and the most difficult to accomplish at the same time, is to create the illusion that the UFO goes behind distant objects. This is the "real killer" as the guy from whom I learned the trick labeled it. In my case I made the UFO go behind a tree. To do it, I cut a piece of carboard with irregularities on the borders, to act as branches, and attached it to the back of a seat. As the light from the flashlight is blocked by the cardboard (inside the room) it creates the desired effect. This is the hardest part of the trick, because you have to carefully create and align the obstacles so that the "shadow" coincides with the external real objects.
Now, on the camera. I chose to use an analog one, as opposed to a digital one, for two main reasons (which I have not checked yet): 1) Analog cameras have lower video resolution, this is desirable for the UFO not to appear too sharp and well defined, 2) Analog cameras are more sensitive to light.
With the help of an assistant, I think it's possible to do a fake of this kind that defies all scrutiny. All UFO convolutions can be done smoothly and in one take, without editing. Other "obstacles" can be added as well.
Well, that's it!. It'll be fun if someone else give it a try to create a better fake of this kind. Just send it to a UFO organization and you'll get headlines

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I'll start another thread later on the Brazilian case, I'd like to know people's take on that. It can be quite puzzling to figure it out, although I suspect it is a fake similar to the one I described.