My son has sharp eyes that pick up on the smallest of details. I consider myself observant, but sometimes it takes me a bit to catch on. Riding on public transit one day, he starts talking about monkeys and bananas. I'm not sure what to think, is he telling me a story? Then he points up and says, "In the picture." Sure enough, there's an ad with monkeys and bananas.
I remember a particular day last summer when I took my son to a community drop-in playgroup. They had a train set that included a few Thomas the Tank Engine characters. They were very old, so old that they either came from a time before the names were printed on the bottom of the train or the names had worn off. I did not know the engines very well at that point, having been introduced to them reluctantly about six months before. My ability to name them depended primarily on their color, and of course several of them were the same color; I didn't yet have their numbers memorized. So I pick up a green engine, no name to help me, and ask my son, "Which one is this, Henry?" He takes it from me and turns it so that he's looking at it squarely in the face. "It's Percy."
When we got home, I checked the train by number and discovered my son was right. Now at that time, all of the trains' faces looked pretty much the same to me. In fact I assumed that the creators pretty much slapped the same faces onto all of the engines. Eventually I could see the slight differences--Gordon has a more pointed nose, for example--but this was immediately obvious to my son.
Sometimes it can feel like a perpetual "I Spy" game, but I truly appreciate that my son is noticing so much.