The following text explains why:

وَالْبَيْضُ الْمَأْخُوذُ مِنْ حَيَوَانٍ طَاهِرٍ وَلَوْ مِنْ غَيْرِ مَأْكُولٍ طَاهِرٌ , وَكَذَا الْمَأْخُوذُ مِنْ مَيْتَةٍ إنْ تَصَلَّبَ وَبَزْرُ الْقَزِّ وَهُوَ الْبَيْضُ الَّذِي يَخْرُجُ مِنْهُ دُودُ الْقَزِّ

The link to the full text of this and a similar article is below.

A much less likely possibility is the seeds of the silk tree (see http://www.bonsai-bci.com/species/albizia.html).

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Note added at 2002-03-26 21:57:51 (GMT)
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- You probably want eggs in plural.

- Note that there is no relation between the silk tree and the silk worm. Except that one is شجرة القز and the other is دود القز. But the worm does not eat from that tree nor live on it, rather it feeds on blackberry leaves ورق التوت.

Best regards,

Alaa Zeineldine