A FEES study is designed to evaluate the swallowing mechanism, and is performed by an otolaryngologist in conjunction with a speech language pathologist (SLP). The study requires the passage of a flexible fiberoptic endoscope into the throat in order to visualize the actual swallow in progress. While the endoscope is in place, the patient is fed foods of varying consistencies colored with food dye. This test allows the examiners to directly observe the movement of the food from the back of the mouth through the throat, and into the esophagus. FEES is more sensitive than VFSS in detecting subtle abnormalities of the swallow mechanism, and provides better anatomic information. However, FEES is not useful in assessing the swallowing mechanism below the entrance of the esophagus. This may require a VFSS or barium swallow test.