Weird shadow through a slatted blind

On this day, the slats of the blind were angled and facing the Sun. This weird spiky, almost digital shadow was projected onto the wall. I have been thinking about how this was made. There is a narrow gap between the slats through which sunlight seems to be coming directly. This would give a normal shadow. Some of the light would be hitting the angled slats, reflecting upwards and then reflecting in my direction from the underside of the slat above. Slats are slightly concave on the underside so this would likely have some kind of focusing effect. Even with these suggestions, I can't see fully how these shadows form.