R. Yehudah b. Betheira says: Opening (a pit) is not like digging, or digging, like opening. What is common to them is that wherever one is liable for guarding it, he is liable for the damage that it causes—so, in all instances, wherever one is liable for guarding, he is liable for the damage. This tells me only of opening and digging. Whence do I derive (the same for) figuring, paneling, plastering or performing any other act in it (to which the damage is attributable)? From "and he not cover it." It is not opening or digging which is the criterion (for liability), but covering (i.e., failure to cover it).