Sour ray is a bacterial fungal infection that eats into the horn, typically in the ray, and causes the horn to rot. It smells sour and the jet is often black and crumbles slightly in the affected area. The horse is often sore, depending on how deep the wound goes. If you press into the area, the horse will often pull the leg in due to pain. The horse can become lame from acid rays. The microorganism responsible is Spherophorus neaophorus, which breaks down the tissue of the ray, so that there is a black-brown float on the surface of the hoof ray.