When I was nine years old, I was opening a can of peaches. Growing up in Indiana in the 1980s, canned peaches were a thing we ate, as well as canned pears and "fruit cocktail" ("…in syrup!")
The can opener did its usual thing, whereby it cut almost the entire way around the top of the can, but then left a tiny sliver of metal still connecting it to the can. My usual means of dealing with this situation was to bend the lid back and forth until the sliver of metal broke. Being a frequent consumer of canned fruit, I had never had a problem with this, so you can imagine my surprise when, a few seconds later, the edge of the lid sliced through to the side of my thumb, just above the knuckle.
It was the worst injury I had experienced up to that point in my life, and still remains among the more serious injuries I have had. While I didn't get stitches, I probably should have–the cut was deep, bled profusely, and thirty years later, I still have a discernible scar on my thumb.
The other thing that I still have more than thirty years later is a lingering fear of can lids. I don't like handling them, I don't even like seeing them–gives me a creeping unease in the pit of my stomach.