During extended capillary flow, a melt now singularity for polyethylene occurs in a narrow temperature interval close to 150 degrees C. This was revealed by a minimum in pressure for constant material throughput. In situ X-ray experiments show only one distinct sharp reflection for polyethylene under these particular conditions. This single reflection was clearly different from the reflections for the orthorhombic phase, and more important, it appears while all orthorhombic reflections vanish. Possibly, the single reflection observed corresponds to a mobile phase which may act as a kind of lubricant for the bulk polyethylene. This mobile phase could reduce the melt flow resistance and therefore induce the extrusion window of reduced flow resistance.