We can feel the elements outdoors--cold and warm, hard ice and soft snow, breezy or still, wet or dry.
The Buddha instructs us to notice the elements in our body. The hard--bones, finger nails, teeth--the so-called earth element. The wet--blood, sweat, tears, and saliva--the water element. The hot or cool--the so-called fire element. And the breath or passing gas--the air element.
We take a drink of water and swallow. We know the water goes down a tube, through various ponds (e.g., the stomach and bladder), and then down a long canal (the intestine), and an even smaller canal (the urethra), before water pours out of our torsos.
That water wasn't "me" before it entered my body. And it wasn't "me" when it exited. Was that water "element" ever me? How is "our" inner water different from outer water?