A classmate drinks soft iced black tea and sucks the straw quickly with his mouth, and the bottle will shrink. What is the reason for the shriveled soft package?

To put it simply, before smoking, the contents in the box are composed of two parts, one is liquid, the other is gas, and the pressure of the gas is roughly the same as that of the outside atmosphere, so the box is basically the same inside and outside pressure, and the box will not be squashed or burst.

After smoking, most of the liquid is sucked away, and the volume of liquid is bound to be occupied by gas. That is to say, the gas expands, and the total amount of gas is almost unchanged. In this case, the pressure of the gas will drop, resulting in a pressure difference inside and outside the box. If the box can't stand the pressure difference, it will be squashed, so the gas volume in the box will decrease and the pressure will increase until it is equal to the air pressure outside.