Seeing things that aren't there (personal experience)

(I'm not quite sure if this is the correct forum to post this, but I'll let the mods figure that one out).

Anyway, this happened while I was at work today. Not to give too much boring detail, my job entails performing field inspections of equipment. Anyway, my car was parked on a residential street, and my partner was out doing the inspection while I waited in the car. I was sort of zoning out when I noticed a very strange creature hanging from a tree. It was probably the size of a large cat and looked sort of like a white-furred Gremlin (from the movie of the same name). Since I wasn't exactly focused, it took me a second to realize this wasn't normal .

I jumped a little, a blinked. It was gone. What was in it's palce was a small branch and leaves in the same general shape of the gremlin. Keep in mind, I saw a solid, white creature with detail such as claws, eyes, and teeth. The leaves were green and not exactly opaque.

I guess what I'm saying is, I never really understood how people could see things clearly that weren't actually there. Now that it's happened to me, I can sort of understand people who say they've seen Bigfoot or Nessie clearly for a moment, and then see it 'dart back into the woods/water'. Not that I'm saying this has caused me to disbelieve in those things, but I understand how many people who give truthful reports of sightings really just saw something in their heads.

Just figured I'd share this with you. Comments or opinions welcome.