The upper pitchers of N. lowii are unusual in that they have a reflexed lid, which exposes numerous bristles on its underside. A white substance often accumulates amongst these bristles, the identity of which has been the subject of some debate. In the 1960s, J. Harrison assumed that these white beads were snail eggs. E. J. H. Corner, who led the 1961 and 1964 Royal Society Expeditions to Mount Kinabalu, wrote the following: