For this blend file I have a curve with many vertices that form a consistent smooth path. I'm animating a walking spider along the curve, it follows the curve perfectly position-wise, and "follow curve" is also checked to enable rotation. I also pressed "alt+g" to make sure it's position is at its default and everything is set how it should be.
But, for seemingly no reason whatsoever, between literally just one frame and another, there are these extremely intense changes in rotation that make the spider rotated completed off its axis for the rest of the path animation as it moves. When I played with the curve in edit mode, I have no idea why this happens, but tiny slight changes in a vertex location have this extremely devastating effect on the spider's rotation to the point where it just flips completely around it's axis completely. How do I prevent this sort of thing from happening? It's a completely smooth curve, all of the arrows have a smooth transition in their orientation from one another, I see no reason for this. A similar thing occasionally happens when I'm rigging bones.