I got into an interesting discussion with the owner of the local glass company the other day about glass they use in zoos. They glue sheets of it together to make the window displays and it is super strong stuff. He relayed a story of a zoo that had two 1/4 thick pieces of glass glued together to form a 1/2 inch piece. A big cat "attacked" the glass and it wobbled like crazy but held. The glass was not up to code. Scary...