Sand impaction is true for lizards. Not sure about snakes, since their digestive process is different.
My experiences with repti-sand:
When I had a beardie year's ago, I had her on sand for a while. It was always in her eyes and they always looked weepy, as did her nose.
When I first got my rosy boa, I had him on sand. It was always packed under his scales and around his eyes. His scales always looked scratched and dehydrated.
I changed substrates...
I think most sand made for reptiles is too fine, making easy to get under scales etc. It's dusty, which can also cause RI's. It clumps like kitty litter, which causes impaction.
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