cellio | daf bit: Bava Kama 51

From the torah we learn that if one digs a pit on public land and an animal falls in it and dies, the one who opened the pit is liable. A mishna explains that this includes pits, ditches, trenches, and similar constructs, so long as they are at least 10 handbreadths deep. (The rabbis consider this the depth at which falling in is fatal.) The next mishna then talks about cases of joint digging: if two people dug, one after the other, and death results, who is liable? The mishna says the second digger; the g'mara explores this more and concludes that everybody who caused the pit to be at least 10 handbreadths, or who found it in that state and left it thus, is liable. So if somebody digs to nine handbreadths and then somebody else comes along and digs one more, the latter is liable, but if the first man dug to ten, both are. (50b-51)