If you are able to read corporal language it's a piece of cake to notice when somebody is bluffing.
Although it may seem out of topic, the best way of learning corporal language is from girls, they are experts at it and once you start watching them you begin to understand that they speak in a "secret" language.
So focusing on arm movements is just a part of the whole you can read from players, but the hard thing is that players always try to control these aspects so the less they know about corporal language the better is for you to read them. I would recommend you watching also the fingers and the hands, specially noting if there is any nervous impulse.