Horseback Riding
Horses are terrifying in general—just throwing that out there before we factor in the people who ride them. Horses are unstoppable thousand-pound death machines that are way more difficult to control than, say, a car. You can't wear a reliable seatbelt here either. It's just you, the horse, and the ground.
Crunching the Numbers
Death by horseback isn't outrageously common, but it's definitely a possibility that you need to factor in every time you hop onto a horse. If you get bucked off of your horse, you will most likely get trampled, which will probably kill you. Horses kill upwards of 100 people per year. Also, never look them in the eye.