Need help to identify some weird "stuff" inside concrete walls

[MiamiCuse]

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:

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:

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

[Robert Allison]

Looks like a termite barrier. May have been used to grout just the upper blocks in the wall, also, or it may have insulation above it.

[nmbexcuse]

Thanks Robert. Mystery is solved. I was told it is a cavity cap. Metal sheets laid on across the bottom of the top course of concrete block so when they poured the concrete tie beam it will not run down the holes below.