Why is popcorn one of the only foods that can cause an appendix to rupture? How does it cause this? What other foods could cause this? Gi docs?

Not true. Appendiceal rupture has nothing to do with the kinds of food you eat. This is an old wive's tale. Rupture is caused by a combination of pressure and erosion of bacteria through the wall of the appendix or surrounding tissue. You may eat all the popcorn you wish.