What makes up feces?

Undigested food: After your intestinal track does its magic, extracting the nutritional and energetic elements from what you eat, then what is left over is concentrated in your colon and passes out as feces. This is true throughout the animal kingdom.

Undigested stuff: Feces is a mixture of bacteria, pigments (bile and food pigments), a little (or a lot) of fluid, and undigested fiber, etc. From the diet.