Back in the Pleistocene, canned sodas had pull-tops. When you pulled the aluminum ring, a strip of aluminum was pulled out of the top of the can, and you were left with a ring of aluminum with a tail.The question was what to do with it. Some people dropped it onto the ground, and some put it back in the can. (There seemed to be no middle ground.) The problem there was two people swallowed tabs that they had dropped back in the can, and one person breathed one in.
On the basis of the litter and the three people's unfortunate accidents, can manufacturers switched to pull-tabs that stayed on the can, but it takes just a twist, and it comes off.
This study identified 19 cases of accidental swallowing of pull tabs in 16 years in one hospital in Cincinnati. It was mostly teenagers. Four of the kids were under 5, and the mean age was 8.5. Only 4 of the 19 could be seen on x-ray. It seems the little tabs are hard to see on an x-ray unless they are actually in the stomach.
There are more of them, but they are less sharp on the edges. I wonder if any of these 19 cases involved serious injury.