The fact that human beings have created a series of shapes in the form of symbols which, using the right combination, unlock and delineate our thoughts and emotions. We unenthusiastically call these "words".
Laughter. A sort of whinnying noise our body makes when it loudly exhales in response to a stimulus which is funny. The average baby does this 300 times per day.
What other ordinary things are there that often go unremarked, but are quite marvelous, unusual and/or impressive when you think about them