"Frah-gee-lay"

This episode neglects to tell us what is so terribly important about a big piece of sheet glass, something we take for granted.

Sheet glass was traditionally made by creating glass "cylinders", which were cut and rolled (not very) flat. The result was a decidedly "warped" view of the world.

https://en.wikipedia.org/wiki/Float_glass

It was the development of float glass that made possible undistorted glass sheets. This is what the French restaurateur wants -- a perfect view of what's going on in his establishment -- and why he's so afraid of such an expensive piece of glass being broken.

Note that the restaurateur is played by a nominally "German" actor, Werner Klemperer!