I'd suggest that paper is a safer alternative cheaper and basically the same with out the risk of ingestion. I have never heard of a snake that has impacted due to wood chips but it would not surprise me either. I can say that in my area (500 000 population) my vet has had 3 cases of paper towel ingestion in the past 2 years, all fatal. Personally, the expense (is any substrate more expensive?) and the fact there is a risk however small make it a poor choice based on my logic. Others may have some valid reasons why they choose it that over rides the issues I see. My opinion is to avoid it there are lots of other alternatives that carry lower risks.