Thick glass, gently sloping shoulders and a deep punt (the indentation on the underside) are necessary as the pressure inside the bottle is three times of the pressure inside an average car tyre.

• 厚厚的玻璃、倾斜的瓶肩、和深陷的瓶底都是必须的，因为瓶内的压力是普通汽车车胎压力的三倍。