People also tend to blink more rapidly "eye flutter" as they're telling a lie. You can trust someone who has told small lies or has lied to not hurt your feelings. Either they are both lying, or the person has unusual body language and is telling the truth. Here is a discussion of each. This may seem like they're lying, but they're often just shocked or ashamed to be put at the center of attention unexpectedly. A Anonymous Feb 11,
They often stop mid-sentence, restart and fail to finish sentences.
Seven Facial Characteristics of Liars
Some people do what actors do: Fox Aug 13, What if I believed someone when she swore she was telling me the truth, but she was really lying? It's hard to keep track of information that isn't truthful. The subject in question might not necessarily be nervous because they're lying. Deliberate expressions may be very brief or very long. Look for other signs too.