A person avoids saying “I”: When people fib about themselves, they tend to use I and me less often than people who are being truthful. Instead, they’ll speak about themselves in the third person (“This is a girl who loves to ski”) or even truncate their language (“Really into listening to jazz”) — anything to give themselves psychological distance from the lie.
A person has an answer for everything: Ask most people what they were doing last week and they’ll have to pause and think about it. That’s even more true of teenagers, who generally don’t have the capacity to tell an elaborate story on the fly. So if someone seems totally rehearsed — there’s zero hesitation before answering a question — well, that’s a dead giveaway.
A person fidgets and fusses for no reason: If someone keeps performing a random physical action that seems unnecessary — cleaning her glasses excessively, retying her shoelaces, or dusting off the (clean) table in front of her — she may be lying. The guilt and anxiety make her restless. That can be particularly true if she is lying to somebody she loves. When a person fibs to a traffic cop, she won’t necessarily fidget a lot. But if she is deceiving her husband, she won’t be able to sit still.
A person proclaims his honesty repeatedly: To sell us on the integrity of their answers, liars often use phrases emphasizing the validity of their statements, like “to tell the truth” and “to be perfectly honest.” These verbal tip-offs frequently invoke religion. Think of expressions like “I swear on a stack of Bibles” and “as God is my witness.” Most truthful people don’t need to go that far.