Airplane Flush Mounted Rivets - How they work. Very relaxing to boot!

After extensive use of automotive rivets, seeing the rivets on an airplane was perplexing. What what holding the airplane skin to frame when the rivets appeared to not have a head. This file, found at my local library, explains it in great detail. This is a very technical file but watching it a few times, it will sink in. Super relaxing film by the way.