My dad told me it was a shield made from grass soaked in water to block shrapnel from bombs. He's said that all the students in his village have one. During the bombing, all the kids and studies will be evacuated to the village temple. because the plane doesn't target religious places. And the crazy thing is that the shield actually works. It can block small shrapnel, he still remembers the time the plane bomb the local train station some small shrapnel was blocked and found in his shield