There might be a couple of things. It also depends on the person, and the situation.If they are a BAD lier.Will not make eye contact, they will change the topic, ocasanally swet if it is a big lie,...
1.He doesn't speak Clearly.
Mumbling and talking faster then normal could signify that hes desperately trying to rush past answering your questions. 2.He chooses his words carefully.Liars wont use...
You don't always know for sure, so it is a good idea to be friends for a very long time unless you are well into your 30's and want to take your chances.