In order to show backflow occurring in the saliva ejector, colored water was sucked into the vacuum line. The end of the saliva ejector was plugged repeatedly using a person's thumb. The video shows backflow occurring into the Safe-Flo Saliva EjectorTM. The Safe-Flo valve snaps shut when the airflow is blocked and prevents the backflow from getting through the saliva ejector and into a patient's mouth. See the "Product Overview" link above to see a short presentation on the cross contamination issue and the Safe-Flo Saliva EjectorTM.