When conducting bombing campaigns on residential areas in Gaza, Israel typically attempts to give residents notice ahead of time in the form of phone calls or leaflets. What you see in this Roof Knock video is the final notice — an explosive roof knock. After the initial warning hit, Israel follows up with a full payload, leveling the building.
This is illogical. If there are militants in the building, they too would be warned by such a knock. In fact they would be better informed of its meaning than civilians. It sounds like the Israelis are engaged in psychological warfare and destruction of civilian property, or are trying to assuage their consciences for killing kids. This is typical bully behaviour, blaming the victim for his suffering.~ Roedy (1948-02-04 age:70) source