Horses are remarkable in the spectrum of facial expressions that they can exhibit. But have you ever wondered why they change their expression? Or asked yourself why your horse always seems “grumpy” when tacked up? Here at the Centre for Equine Studies at Animal Health Trust in Newmarket, we recently developed an ethogram — a description of behaviour (see below) — for the facial expressions of ridden horses. Using this ethogram, we investigated whether we could determine the likely presence or absence of lameness based on analysis of a series of photos for each lame and sound horse.