How to tell someone's lying to you just by looking at them

Discerning a lie from a truth is no easy feat, especially when you're dealing wit a skilled liar.

To detect high-stakes lies, the FBI frequently look to a combination of facial expressions, body language, and verbal indicators as signals, or "tells," that someone is lying.

Mark Bouton, an FBI agent for 30 years and author of "How to Spot Lies Like the FBI," tells Business Insider that he used certain tells to help identify Timothy McVeigh as a suspect in the Oklahoma City bombing.

But anyone can use body language and facial cues to detect lies - you just need to know what to look out for.

To start, Bouton says it's important to understand how the person in question normally acts.

"It's best to observe someone for a while as you make small talk or ask innocuous questions, in order to see what his usual reactions are, including tics he may have," Bouton says. "Then if he exhibits several lying indicators when you ask more pointed or suggestive questions, and these are not ones he previously performed, you can be confident that he's likely lying."

Some cues are caused by nervousness, some by chemical reactions, and others by physical reactions. Here's some of the body language and facial expression Bouton looks out for: