Some people tell lies so naturally that you might not even notice the small changes in facial expressions and body language. Do you know what are the little expressions and body language to spot a liar? Have you caught one before? If yes, how did you tell?
Body language, and it's all in the eyes. Lack of eye contact, and eyes moving in one direction (I think we learn't in NLP it was to the left, need to double check that), as well as fidgeting and soft tone with a lot of "ums" and "ahs" thrown in.