possible ufo seen.

Many years ago, I saw this thing in my backyard. It looked like a garbage can lid, but it flew down, turned a little, then went back up and behind some trees. The winds were calm this day. This possible ufo was about 10 ft above me. I didn't see it after that, but many years later, I saw similar to this, but this time, it was at night. In front of my house there were 2 large trees and I saw like a disc of some sort like skip across the trees, and I haven't seen it since. Any idea what these were?

also, it made no sound.

Kinda freaky. I'd say that they're definitely Unidentified, but what they are in reality is well beyond my scope of conjecture. If I were forced into a decision, I'd say terrestrial in origin. Spy drones for the gov't. No joke. Peace.

Why would they spy on me?

It was silver colored and I could tell easily that it was made of metal. It was about the size of a metal garbage can lid. Could UFO's be this small? Actually, it was probably more like 4-5 ft above me and about 10 ft off the ground. Maybe the size of it would increase a little if it were to land. Maybe I should've taken a rock and threw it at it from a safe distance.

Possible answers:

It could have been a probe of some sort.
Some people have reported very small aliens too, although this is rarely encountered.
Warping space time also causes a distortion of perceptions.