I have been using aspen as a substrate. So far, I have not had any problems with it whatsoever. I feed my snakes in a separate container to avoid ingestion; however, I recently caught two new snakes and they are not yet comfortable eating in a separate container, but they will eat in their enclosure. Small bits of aspen cling to their food and they swallow it. I'm very concerned about this.

Aside from being sharp and puncturing innards, what other problems can occur from ingesting aspen?
Does the size of the pieces ingested matter? The pieces my snakes are swallowing are small.

If this is a major problem, does anybody have any suggestions what I should do? I would prefer to avoid changing substrate, but if I must: What would be a safe, cheap and attractive alternative?

Any information on aspen and it's potential problems is appreciated. Thank you!