We've seen bb guns shoot through goggles before but where does to glass go in the hole?

When those bb's hit safety goggles, they dont usually just cut a clean circle out. Most of those lenses are made of polycarbonate, which is a tough plastic rather than actual glass. When a bb punches through, it mostly pushes the material inward and creates a jagged, crater-like hole. Some of the plastic debris gets pushed into the eye socket along with the bb, and some of it just chips off and sprays behind the lens.

I've seen this happen on job sites a few times. Because the material is plastic, it tends to stretch and tear before it finally gives way. You'll usually find little plastic flakes trapped between the lens and the face, and honestly, that's why they can be so dangerous. It's not just the bb that hits you, but those sharp little shards of plastic getting driven right into your eye.