Step 1. In the first video a manual tracking of head and shoulders is carried out: the cloud of red points determines the Regions Of Interest (ROIs) head and shoulders are located in. The blue dots are the geometrical barycenters of each cloud. In the second video, shoulders are automatically tracked by means of small green markers.

Step 2. Body Laughter Index is computed by looking at shoulders' correlation and energy: high correlation and energy indicate that the probability of laughter is high; this information is acknowledged only if the shoulders' movement is periodic.