When you eat, your body notices and hurries along the food you ate in the past to make room for it. With spicy food in particular, it hurries a lot, which means the large intestine doesn't get enough time to absorb enough water: that's why it's runny even though those particular feces don't contain the spicy food.
SonicN t1_ja9awng wrote
Reply to ELI5: If food takes 6-8 hours to fully digest and make it to the small intestine, how come food you eat now affects the qualities of feces from food eaten 8 hours ago (i.e. having to use the toilet soon after eating)? by [deleted]
When you eat, your body notices and hurries along the food you ate in the past to make room for it. With spicy food in particular, it hurries a lot, which means the large intestine doesn't get enough time to absorb enough water: that's why it's runny even though those particular feces don't contain the spicy food.