And as best I know, no one has come up with a good theory why certain snakes developed keeled versus smooth scales. There are no commonalities either - such as not all water snakes have smooth or keeled scales, not all venomous snakes have smooth versus keeled, not all desert habitat snakes or jungle habitat snakes, etc etc. Nearly all vipers have keeled scales but not all. One theory is light reflextion - smooth scales are shiny, keeled are not which could aid in camouflage. That means snakes that are ambush hunters theoretically would favor keeled scales and vice versa but there's plenty of contradictions to both. I love nature, I doubt we'll ever figure it all out.
(I did not carve the goose)