A few decades ago I used to keep my corn snakes on sand. I figured that it was a nice looking substrate and if they swallowed some, no big deal it would just pass through. I ended up losing a number of small corns however. They would be eating fine, then they would quit eating and eventually start looking lumpy. When they died, I cut them open and found they were stuffed with sand. Even though the grains were small enough that it 'should' have been able to pass right though them, it appeared that the sand had stuck to the lining of the intestines and just built up over time until they were completely blocked. I switched to non particulate substrates after that.

I also have a friend who is a vet that did a necropsy on a burm. The burm quit eating and eventually lost a lot of weight, had no muscle tone and eventually had to be put down. The burm had been kept on wood chips for years and always ate a bunch of wood chips with every meal. But since he kept pooping fine it was assumed by the owner that they were just passing though and not causing any kind of blockage. After the animal died and was cut open, she found what was REALLY happening to those wood chips. Wood is not digestible so it doesn't go away, but it does break down into slivers. The slivers were piercing the intestinal walls and lodging in the muscle surrounding the stomach and intestines. After so many years of this the muscle looked like gray gelatin that was impregnated with millions of tiny wood slivers.

Mark