Make several small incisions along the belly, push and stretch the prawn from its back as much as you like, and as you crush it, listen to the sound of the tearing muscle.
伸ばし方としては腹側に何箇所か小さい切れ込みを入れ、背中から押しつぶすように、腹のスジが「プチプチ」と切れるように、好みの大きさになるまで「つぶし伸ばす」。