Peristalsis is a wave of ring-shaped muscle contraction that squeezes a tube from behind the food, pushing it forward — the same way toothpaste moves when you roll the tube. The esophagus fires one such wave per swallow (about 8-10 seconds to reach the stomach); the small intestine mostly uses local "segmentation" contractions to mix and slowly advance chyme; the large intestine holds still for long stretches and only sweeps forward a few times a day with slow "mass movements".
The peristalsis rate slider scales how often contraction rings fire and how quickly the wave travels — turning it up shortens the estimated real-world transit time shown at right, matching how stronger gut motility speeds up digestion (and weaker motility, as in some GI disorders, slows it down).
Food type changes how long food actually dwells at each stage: liquids leave the stomach fastest (gastric half-emptying around an hour), an average mixed solid meal takes two to four hours, and a high-fat meal delays gastric emptying the most because fat triggers hormones (like CCK) that deliberately slow the stomach so the small intestine and liver have time to process the fat. Small-intestine transit is fairly constant near 3-5 hours regardless of meal; the large intestine is by far the slowest stage, holding waste for 12-30+ hours while reabsorbing water — which is why total gut transit ranges anywhere from about 24 to 72 hours.