Seeing long, thin worm segments or rice-like proglottid sacs points to intestinal worms.
Worms
Whole pieces of food may mean an upset stomach, eating too fast, or poor chewing.
Undigested Food
Fresh blood or black, tarry feces indicates GI bleeds warranting prompt veterinary care.
Blood
Ingested bones that splinter can be visible after passing through or cause constipation.
Bones
Swallowed fruit pits, corn kernels, or other seeds may appear after passing through.
Seeds or Pits
Eaten grass, sticks, rocks, socks, etc. eventually get passed in poop.
Rocks or Non-Food Items
Shedding season leads to dogs ingesting and passing fur in stool.
Hair