Israel's "knock on roof" technique consists of shooting a building with a warhead-less rocket as a final warning before blowing it to bits.
The idea is that the people living in the building have a few moments to evacuate the premises before the major onslaught.
Apparently, according to Haaretz, Israel also calls the family by phone to warn them of the first mortar.
Amnesty International has decried “roof knocking,” saying it in no way constitutes an “effective warning.”
“There is no way that firing a missile at a civilian home can constitute an effective ‘warning.’ Amnesty International has documented cases of civilians killed or injured by such missiles in previous Israeli military operations on the Gaza Strip,” said Philip Luther, director of Amnesty's Middle East and North Africa program.