وَكَأَنَّ رُبًّا أَوْ كُحَيْلًا مُعَقَّدًا حَشَّ الْوَقُودُ بِهِ جَوَانِبَ قُمْقُمِ
It is as though thickened syrup or tar were being heated, with fuel blazing around the sides of a cooking vessel.
Rubb is a reduced thick substance and kuḥayl refers here to tar-like black dressing. Muʿaqqadan denotes thickening by heating, and qumqum is a vessel. This image continues into the next verse: the comparison prepares us for a substance flowing behind the camel’s ear.