Lines on the Leaf, not Leaves on the Line

I have no idea why some leaves develop these ridges across them and end up folded or twisted while others remain perfectly smooth and straight. I'm not sure I want to know. I just know that my eye is drawn to them.

I had my first blip related injury today trying to capture this. I crouched down on top of a nettle that I hadn't noticed. Never mind, it could have been worse. I could have fallen into the pond.