"The main one is that first contact appears to have happened at different points. It could be that previous instances were covered up, but we all remember different dates: the 1990s, the 1940s, earlier than that in a case or two. That, and superheroes---they exist on different worlds, but we haven't heard of the sets from others' Earths."

Billy folds his hands behind his back, frowning. Nothing that too severely affected the course of the planet, it seemed, but it was still worrisome.