Let's see...
Horse might get organs crushed if it lays down too long. (I heard this before.)
Horses can be dangerous yet they can get scared easily.
Mares can have more than 2 or 3 foals in their lifetime.
Horses don't like corn as I heard, they're more of the animal version of health nuts.
Horses always sleep standing up, but foals have to outgrow sleeping on the ground.
Teenaged horses are called coals for males and fillies for females.
Yearlings are horses that are not yet teens yet not foals as I heard. (I'm guessing smaller than coals/fillies?)
I'm not sure if I got my facts right completely. I know I probably know more in appropriate facts but... yeah. o3o