|excerpt of the infographic on the Randommization blog|
In theory, your eyes, your body language, your word choices, etc. can all give away the fact that you're trying to keep the truth hidden. The linked infographic describes some of the ways people think they can detect such deception.
This isn't the full infographic here, by the way, it's just one small part of a much larger infographic which I could not adequately reproduce using picasa web albums (which resizes images that are too big). According to both Buzzfeed and Jezebel the full infographic is supposed to be here, but as of writing apparently something's busted in the series of tubes that is the internet because where the infographic is is just a broken frame pointing to AWS. It's a good thing this copy can be found on the Randommization blog