On casting contagious fog, a cloud of fog was created. This cloud had a radius of 30 feet (9 meters) and a height of 20 feet (6 meters) and had a number properties. Overall, the fog looked like the one created by a fog cloud spell and moved away from the caster like a cloud created by means of the cloudkill spell. The cloud was heavier than air, allowing it to seep through cracks of any size, but it could not enter any liquid and the spell was actually impossible to cast underwater. Furthermore, the cloud carried a disease. People who touched it were in danger of contracting the shakes with no incubation period at all.