The teapot is a container with an open top and a communicating bottom, so the teapot is made according to the principle of the communicator.

Opening holes in coconuts can make the air circulate more smoothly. When drinking, you can inhale and exhale to make the pressure inside and outside the coconut equal, so that coconut water can be easily sucked out. So this phenomenon is the use of atmospheric pressure.

Therefore, the answer is the communicator; atmospheric pressure