OK this is getting weird, but I need to ask.

Last week I got someone to cut an opening for me for a window...I was
expecting a rectangular hole but he ended up chiseled out this irregular
opening in my concrete block wall. The hole is now covered with a sheet of
plywood from the outside, as you can see here from this image:

http://i173.photobucket.com/albums/w...g/P1010366.jpg

Now, this is not the reason for this post. If I walk closer to this new
window opening, and look up to the inside of the block wall above the
opening, I see this:

http://i173.photobucket.com/albums/w...g/P1010363.jpg

This look like some metal foil with something above it...what is it? Any
idea? The opening is about 28" wide, and if I look up, every block wall
hole has this metal thing in it.

I am tempted to cut into it, but I thought I will ask first in case someone
recognize this as some old way of leak proofing something...

MC