Hamas put civilians on the roofs of targeted buildings

The excellent Mere Rhetoric noticed this. From Ha'aretz:

The IDF believes that about two thirds of Hamas' underground rocket launch sites in the northern Gaza Strip were destroyed in the first round of Air Force sorties, on Saturday.

Additional bunkers were destroyed in the days that followed, after a way was found of striking them when civilians were not in the vicinity.

The IDF has made frequent use of what is known as "knocking on the roof": Militants are warned by phone when a residential building used to store arms will be bombed, and told to vacate the premised together with their neighbors. The weapons caches are hit only after the residents leave.

Hamas has tried placing civilians on the roofs of such buildings when the phone call warning comes in. In these cases, the IDF fired antitank missiles near the building, and in a few cases the residents left.