When you open a carton of milk and pour it out, chances are that it splatters out and spills around. This is because for the milk to come out, air needs to get in. With one opening, the air pushes through the milk trying to get out and the flow becomes turbulent and uneven.
The simple way to prevent this is to make a small opening on the other end which will allow air to enter separately and the milk can flow out smoothly without any splashes and spill!
This video will show you how. Your other options are to make a large hole or to use a collapsible carton or bag.