Cutting the vagus nerve in a ruminate abolishes coordinated reticuloruminal motility. There are also vagal afferents from the rumen to the motility centers which allow stretch receptors and chemoreceptors in the rumen to modulate contractility. Conditions inside the rumen can significantly affect motility. Rumination is regurgitation of ingesta from the reticulum, followed by remastication and reswallowing. It provides for effective mechanical breakdown of roughage and thereby increases substrate surface area to fermentative microbes.
Regurgitation is initiated with a reticular contraction distinct from the primary contraction.
This contraction, in conjunction with relaxation of the distal esophageal sphincter, allows a bolus of ingesta to enter the esophagus. The bolus is carried into the mouth by reverse peristalsis. The fluid in the bolus is squeezed out with the tongue and reswallowed, and the bolus itself is remasticated, then reswallowed. Rumination occurs predominantly when the animal is resting and not eating, but that is a considerable fraction of the animal's lifespan. Fermentation in the rumen generates enormous, even frightening, quantities of gas.