This is the secret to breathing underwater, and it's not using a bamboo tube like in cartoons. Because it doesn't actually work; the water pressure traps the air and will only suffocate you. So how do you do it? But if you can breathe, then put a like: take an upside-down box and sink it underwater so that it traps the air inside. Then breathe through that air pocket, just like Jack Sparrow teaches you.