If two potters were walking one behind the other in the public domain, and the first one stumbled and fell, and then the second one stumbled and fell over the first, the first one is liable for the damages to the second. 

Although the potter lying on the ground caused the damage passively, this is a case of damage inflicted by “man,” since the obstacle was his body. He is consequently liable even for the damage to the second person's utensils. Although stumbling is not negligence, he should have warned the person behind him.