I think it might be accessories or part's of the yukkuris that it ate.
Yugigigiiiiiiiiiigiiigigigi!!!!Yufu!
The gourmet Reimu has elegantly finished eating!Yu? What? Don't do cruel thing to Reimu anymore okay?Yufun! Oh right, please wait for a while. Reimu will give a gift for Reimu who has worked hard for us! Sorry for being kind!Mukyu.
Lets go outside then. There's nothing left here but trashReimu will return Reimu's babies! THey are delicious! Sorry for being kind hearted!Don't worry. The kind Reimu will give this yukkuri a parting gift! It's nothing much, but this is a present from Reimu for Reimu!Fuh, that's delicious. Reimu, are you done eating yet ?