the mystery of the inflating hamburger

I buy frozen burgers because I like to be stocked up for a week or two and have them ready to go when I come home from work. I'm not too brand loyal--if something's on sale, I'll try it out.

I recently bought some Glenmark Cookout Burgers. The package states "homestyle thickness" and "our biggest burger." Okay, fair enough. There's 8 in a box. The first thing I notice is that it's more of a rectangle than a circle, or even a square. It's basically shaped like a deck of cards.

Prior to the incident, I had cooked a few, and thought they were fine. Nothing outstanding, but perfectly suitable. And then one day I put one on the George Foreman and I had my sweet corn going in the microwave. After a few minutes I opened up the grill and noticed that it was puffing up, like a balloon. I put the grill down and cooked it longer. I lifted it up and again saw it almost inflating. I poked it with a spatula and tongs, and I could flatten it to normal thickness, but then when I let go of it, it inflated up again.

I wasn't sure if it was full of blood, or if it was going to explode, or what. But it looked done. So I put it on my plate, and cut into it. This is what I found:

In case you can't tell, this burger was hollow. Or at least, a definite air pocket. It looked like a pita. Or a chicken cordon blue without out the stuffing.

I ate it and it tasted just fine. I felt a little gypped but I suppose it was the same thickness. In fact, this could be a genius marketing ploy: DIY stuffed burgers--cook and then stuff with cheese and bacon and barbecue sauce for an inside-out masterpiece!