'well , ' said peavie , uncomfortably , 'what you do is , you take some corn , and you put it in , say , a number 3 crucible , with some cooking oil , you see , and then you put a plate or something on top of it , and when you heat it up it goes bang , i mean , not seriously bang , and when it 's stopped banging you take the plate off and it 's metamorphosed into these , er , things ... ' he looked at their uncomprehending faces .