What do you mean by "machine" and "burial" in couplets?

During War of Resistance against Japanese Aggression, the Japanese bombed indiscriminately. Chen Yinque, a China scholar, suffered from operating a bomb shelter when he was teaching at Kunming Branch of National Southwest Associated University, so he made a couplet: "Take advantage of the situation and bury in peace." "Play it by ear" originally refers to improvising and acting by ear, but it refers to "acting when you see an airplane"; "It is safe to be buried underground" originally meant that it was reassuring to bury the dead, but this meant that it was safe to enter the bomb shelter.