The mating act of two horses is shown: A stallion (intact male horse) approaches a mare (female horse) and sniffs her flanks and genitals, then mounts the mare and covers her before descending.

The fact that in this case there is a rider on the female horse is not some perverted form sexual or sodomist pleasure, but purely accidental. The attention the stallion is paying to the mare is unplanned and undesired. This highly dangerous scenario can happen in reality when a mare is ridden in a location where a stallion is allowed to roam.