At Psychology Today, "Top 10 Secrets of Effective Liars":
One of the reasons most people make bad liars is that they find lying a deeply unpleasant activity. Fear and guilt are evident in their facial expressions. They want to get the process over as quickly as possible, so they show relief when their interrogator changes the topic. That's a dead giveaway. Really good liars, on the other hand, actually enjoy the process of deceiving other people. "The best liars don't show any shame or remorse because they don't feel it," says Cohen. "They get a thrill out of actively misleading others. They're good at it, and they enjoy the challenge."Via Instapundit.