The defecation reflex causes the rectal wall muscles to contract—that is, squeeze—at the same time the anal sphincter muscles relax. To the conscious mind this registers as urgency—somewhere between “Hello” and “Drop what you’re doing.” The larger or more liquid the load, the more pressing the urge and the tougher it is to hold back. Water will leak out a very small opening. As one gut expert put it, “Not even the sphincter of Hercules can hold back water.” Take this to its end point and you have the simple saline enema—and an urgency that is not easily, if at all, overridden.
