The only substrate I have ever heard to be a massive issue being ingested is paper towel. I have had a one eyed snake eat a lot (a lot!!) of aspen and she did develop constipation after this but I mean two full mouthfuls her aim is very very poor. I have seen a few splinters stuck from wood chip substrates but nothing overly serious. Like Jen I use a coco peat substrate (very similar to some orchid mediums) I have never had too many issues with it since switching well over 2 years ago. It has the added bonus in being about 17¢ a full cleaning.