No matter how many crown tail bettas my cousin or I have bought, they all have this funky spinal curve down by their tail. The veils we have do not have this. If you look at the fish from above, his body is straight til just before the tail fin it curves slightly. I have included pictures of my bettas with this. Is it genetics maybe? Do all CT's have this? Is it from being in a cup all the way from Thailand?
Forrest is the oldest, so it is very prominent and you can see the bulging (towards the camera) where it starts.
These two are under an inch long, so I pointed out where it is.