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Thank you for answering! I sort of expected it, since I never heard of any herbivorous snakes - but I'm no expert.
And yet its surprising, because there are so many different snake species and not all of them are big venomous beasts. I mean, I wouldn't expect them to eat grass or other green stuff, but perhaps fruits or seeds with a high fat content or so.
But well, it seems they managed to survive without going in that direction.