What can be worse than a prison's protection?

Please don't look at the photos especially if you are about to eat something or have eaten your fill....
Using broken glass to line or protect the walls of homes were very common in the past.
Let's say it was acceptable in the 1960's.
In the past, the glass shards were relatively shallow and smaller.
But wow! The glass shards here are certainly meant to "murder" someone! Very scary stuff!