When he was two or three, my son got his hand trapped in one of the old-style tins that we had opened, emptied, and then shoved the lid down into. When he put his hand in and tried to pull it out, the lid had cut into the base of his thumb, and the more he pulled the deeper it went. To get his hand out again, we first had push it further in so that we could push the lid aside. Try explaining that to a screaming toddler.
I still squash tins closed to this day.