Ultrasonic friction modulation of the bare fingertip touching a glass plate has the potential of bringing haptic feedback to touchscreens. The physical underpinning of the phenomena that creates this reduction of friction has been elusive to researchers. In order to draw a greater understanding of the physics at play, we developed an imaging system that is able to capture the motion of the skin with a 1µs resolution. The results from this study showed that the skin is actually bouncing on an air cushion. This air cushion limits the contact between the plate and the skin thus reducing the friction experienced by a bare fingertip.