Scales on a snake howto

[Fabrice]

I think I found something approaching setting the "surface element" to "From closest surface normal".
It is near the effect I was lookin for, the scales follow the spline's deformation.
https://imgur.com/k0suTqv

But there are still some of the scales that are reverse (in red), 
I dont understand why?

Or Is there a way to delete those reversed one?