硬氣

硬 = 更 + 石 : Maud Younger (y) finds the snake which ate too much (更) in the engine's bathroom ((e)ng4), and it feels miserable. To make the snake feel better Maud massages the snake using two warm stones (石). As Maud massages the snakebshe finds that the snake's belly is really hard (硬).

Mnemonic symbol: a balloon. The Queen of Hearts is disappointed by her balloons. She expected them to float upwards, but in the space station's bathroom, They float randomly in all directions.