"ka-annahunna baydun maknun" (as if they were hidden pearls). Some interpreters say that by "bayd" (eggs/white things), it is meant: pearls, as in His saying: "And fair ones with wide, lovely eyes, as the likeness of pearls" (al-Waqi'ah: 22-23), hidden in their shells.
﴿كأنهن بيض مَكْنُون﴾ تَفْسِير بَعضهم يَعْنِي بالبيض: اللُّؤْلُؤ، كَقَوْلِه: ﴿وَحُورٌ عِينٌ كَأَمْثَالِ اللُّؤْلُؤِ﴾ مَكْنُون فِي أصدافه.