My 3 year old son in the past 2-3 months has been doing these strange facial grimmaces. At the same time he grimmaces he lifts his arms and contracts them. He does this at least 3 times a day. It will only last a few seconds and he is completly responsive during it. At first we thought he does it when he gets overly excited or angry but I have been noticing it more when he is just sitting around. What do you think?