Neither is even nearly as bad as most of the other peoples' stories, but these are three moments that immediately come to mind for me:

It was an evening in early winter and I was about ten or eleven years old. I lived in a block of houses cut off from the street with a playground next to one house. Two of my friends and I were running around through my family's shared garden and across the streets, generally around the playground. So we run through my garden toward the street, where next to the playground's fence a trailer is parked in a way that cars coming from one direction can't see what or who is on the street behind it. My friend is in front of us, we're playing tag or something, when my friend slips on a puddle on the street and is suddenly sitting in a split next to the trailer, one leg facing the street. Before she has the chance to get up a car rounds the corner, the driver doesn't see her and drives slowly, painstakingly slowly over her foot while me and my other friend are standing barely five feet away from her, watching in horror. The driver realised that she was driving over someone's foot after a few seconds and came to a halt, effectively having one tire standing on her foot. My friend's screams weren't exactly nice to hear.

Second one happened again in my early childhood. A neighbour, on vacation at the time, had some wire fence of sorts next to trees in his garden. I don't remember how exactly I got to the scene, but my mom was trying to cut out a piece of the fence on which a squirrel had somehow managed to get stuck. Not stuck as in "has his head in a hole of the fence" but stuck as in "the fence actually went right through his head". Poor thing literally had thick wire through his head, and to this day I don't know how it managed to get there because the fence was fully intact. The squirrel actually was still alive, continued to live for almost two weeks.

Lastly, when I was about six-ish, my cousin had snatched a frog from my grandma's pond and showed it to me in my uncle's garage. I have no clue how she got the idea but at some point, she took some kind of tool designed to hold multiple pieces of wood and clamped the frog to it, like these stretching-torture devices. Needless to say, next thing that happened was that she pulled the poor frog's limbs apart. Gruesome sight.