As a result, the animal's faeces passes through containing a lot of undigested food particles. (petsmagazine.com.sg)
Occasionally, you may see bits of undigested food in your baby's poo, or it may even be different colors. (babygaga.com)
I'd read that poor stomach acid hinders protein digestion, thus allowing undigested protein to enter into the bloodstream making it acidic. (hairlossrevolution.com)