peristalsis
"This is when your airway passage and the rest of your digestive system meet. The bolus continues into the esophagus where it is pushed along by peristalsis. Peristalsis is like using your hands to push a marble down a smalll rubber tube. Then the bolus enters the stomach and into the gastric juice. The bolus is broken down into a liquid called chyme. The chyme then leaves the stomach and is emptied into the small intestine. The first part of the intestine is called the duodenum. The digestion process is done once the food particles leave the duodenum."
Or maybe lake waves or wind waves. Anyhow, when water makes waves in a given direction the stuff floating in the water will move in the direction of the wave. The motion is up and down but in the vertical dimension but straight in the horizontal dimension.
METAMIA is a free database of analogy and metaphor. Anyone can contribute or search. The subject matter can be anything. Science is popular, but poetry is encouraged. The goal is to integrate our fluid muses with the stark literalism of a relational database. Metamia is like a girdle for your muses, a cognitive girdle.