"Small horseman and figures mounted on serpents." That's what my guidebook says is pictured in this lintel over a doorway in one of north towers of Prah Ko. I think that's a "kala" or monster head in the middle ... apparently the Kala was quite famished and asked the Hindu god Vishnu for someone nice to chow down on. Vishnu was angered and, since gods are quite creative and delightfully perverse with their punishments as we of all different religions know very well, he ordered the Kala to eat itself. Except it couldn't very well eat it's own head could it, so that's all that's left. The Kala is supposed to protect temples so you see it a lot over doorways. FTR this is much more impressive to see in real life.