Horses are somewhat famous for laughing.
For example, in The Book of Job
we have the Lord bragging about this marvelous creation of his;
.....the horse
who hears the horn, smells the battle, the thunder and the shouting
.....and saith "Ha, ha!"
From a purely human point of view
..... it's hard to see what's so hilarious
given the rein, the bit hard in the mouth,
.....the bridle, the lacerating spurs, the crop,
.....and all that.
But then, I'm not a horse.