I saw a red squirrel in the park beside the Aachen casino a week ago. It was more brown than red. I did a double take, and wrote in my mind the sentence, "I'm seeing a red squirrel. I thought they were extinct, out-competed by the grays. It's small."
It was on the ground in front of the trees in a clearing, moving right. Seeing a unicorn would've been scarcely less surprising. I didn't think I'd ever see a red squirrel, except in popular science stories about population dynamics. I wasn't sure what I was seeing, but I looked, and it was a squirrel, and more red than gray.
It startled away. Though - it was so far away that it perhaps didn't even see me. Seeing a red squirrel was a surprise for me, but seeing another human could be no surprise to it. It's existence was a surprise to me, but not to it.
It must've moved into the green, but I didn't see it go. My memory had fixed the moment, and my mind was thinking harder than my eyes were looking. I stopped seeing it before it disappeared.