I've been witness to the same UFO 3-4 times. Always happens in the Western sky. Just looks like a star, but suddenly out of the corner of your eye you will see it "drop" and "bounce" down past the horizon. It reminds me of a ball bouncing down stairs but on a two-dimensional scale.

For the longest time I though it was a shooting star. Then I saw a real shooting star, which speeds across the sky not just straight down and back up into the sky and back down past the horizon...

Oh and Coelho, I have also heard / read that Brazil is a goldmine for the chance of seeing a UFO. You just have to keep you eyes to the skies...