This coin had more strands attached before I realized what I was looking at. I tried to wipe off what I thought was some loose lint before taking a closer look. There are still strands embedded. One in the "S" of TRUST resembles a twisted ribbon, moves when nudged with the tip of a toothpick and has a bit of metallic reflectivity, a shadow can be seen below it.
Could it be off of what they use to polish the dies? And would this be called a retained struck through?