Little words are easily overlooked, but these tiny titans often play a significant role in language. Consider our much used (yet almost invisible) set of pronouns. Holding a conversation would be near impossible without them and confusion would reign. I, you, he, she, it, etc. work quietly in the background letting us know who we're talking to or with or about. They're also doing something else in the meantime. They're giving away our secrets.
Find out what they those secrets are in The Secret Life of Pronouns: What Our Words Say About Us by James Pennebaker.
If you like this book, try a few other "secret" titles:
Snoop: What Your Stuff Says About You  by Sam Gosling
Traffic: Why We Drive the Way We Do (and What It Says About Us) by Tom Vanderbilt
You Are What You Wear: What Your Clothes Reveal About You by Jennifer Baumgartner