Mission 33
On page 112 Kamogawa dad says he’s picked up a 八尺玉のかけら. The comment is ignored and then nothing more is said about it.
There is a dictionary entry for 八尺瓊勾玉 (Yasakani no magatama) which is one of the three sacred treasure (imperial regalia of Japan). A magatama is a prehistoric “comma-shaped” bead or jewel which in certain parts of Japan are found in large numbers at excavations. So my guess was that he’s found a fragment of a magatama - and referring to it as a Yasakani tama.
Presumably most people would be interested in such a find (perhaps like finding a fossil fragment?) although Fuchuya is in a grumpy mood and pays no attention.
Or I may be completely wrong. Looking at the picture he could just be half way through eating a croissant…