Géricault was a keen horseman, and his expert understanding of horses' anatomy matched his passion for them. In 1813 he produced several oil studies and finished paintings, possibly including this one, of horses at the Imperial stables at Versailles. These paintings demonstrate close observation and detailed naturalism.
In this picture, we see a fine thoroughbred. Géricault has shown the moment it reacts to a bolt of lightning (in the upper right corner), and presumably, the accompanying clap of thunder. He avoided the more dramatic, and perhaps rather clichéd, image of a horse rearing, instead of showing the animal in profile as it freezes in fear.
Géricault brilliantly captured the sheen of the dappled coat as it is momentarily lit up against the near blackness of the night sky. Using short, staccato strokes of liquid paint, which precisely follow the contours of the horse's body, he created an effect of nervous energy that ripples across its silky surface.