A bit of all three.

I'm a pretty sharp observer of people in general. And I can spot a lie from about a mile away because I had an especially prolific liar (and manipulative, calculating schemer) for a little sister. She wasn't a compulsive liar; she knew exactly what she was doing, and did it anyway.

I also developed a skill at body language and reading eyes, as a natural result of all of this, too.