I'm not going to search for it, but I have seen a video of a guy getting a stick clean through his thigh, which is a potentially fatal injury if you get anywhere near the femoral artery.
When I was riding dirt, my number one concern was impaling hazards. I would always stop to move broken branches off the trail, especially if they were at chest height.
Just imagine how many hundreds of thousands of years we hunted things like mammoths with nothing more than sharpened sticks.