Draw a large circle near the top right side of your paper, and then draw a smaller circle near the bottom left side of your paper.
Connect the 2 circles with 2 curvy lines.
Add a tube at the top of the stomach, and one at the bottom of the stomach. Erase where you see dotted lines.
Draw a curvy rectangle in the middle of the stomach.
Draw waves across the middle of the viewport. Then behind the waves draw squiggly lines that look like wood grain.