What Causes the Gurgle When I Pour Water From a Bottle?
The air trying to get in causes the gurgle. Air has one strong characteristic which stands out above everything else. It wants to go some place else all the time. When it learns of a place where there is no air it wants to go there above all things, and goes at it with a rush.
Now, when you turn a bottle full of water upside down, the water comes out if the cork is out, of course, and as soon as the water starts out the air strives to get in, and every time you hear a gurgle you know the air is getting in. Every gurgle is a battle between the water and the air. Sometimes the air comes and pushes the water back enough to let it slide into the bottle; sometimes the water pushes the air back, and thus they fight back and forth. The water always gets out and the air always gets in. In doing so they make the gurgle.