English: Passage of food bolus through the esophagus of the butterfly Pieris rapae. View (1.3 × 1.0 mm) is a lateral projection through the thorax of the butterfly (mass ~50 mg), with food moving from anterior (upper right) to posterior (lower left). The butterfly was feeding on a mixture of sugar water and iodine compound (Isovue). X-ray energy (33.2 keV) was tuned just above the K-edge for iodine, making the food bolus appear dark. This clip demonstrates how synchrotron imaging can be used to visualize internal food transport during feeding in small animals. Note that the esophagus is collapsed until the bolus passes through; the light structure running along the same diagonal axis is a tracheal tube. From this clip, it can be seen that the bolus is tapered at both ends and is transported at a speed of ~1.5 mm/s.