This paper presents preliminary results on an investigation into a visual illusion observed in health care. The illusion is demonstrated in radiological imaging and may have impli- cations for patient safety. A URL to a video of a Positron Emission Tomography (PET) scan image was circulated and participants reported the type of movement they observed in the video. There is a wide variation with respect to the observations reported, which appears to be independent of gender or age differences. The clinical significance of this finding is discussed and plans for further investigation of the phenomenon are outlined.