User blog comment:Emptylord/Leaked Champion: Vel'Koz/@comment-9705522-20140203160407/@comment-7709681-20140203172249

I just said that they guarded the entrances, not how this originated. Additionally, Cho'Gath nor Kha'Zix were summoned they entered by themselves, is possible for they to open their own rifts aswell for rifts to be an rare happening that "ocurrs naturally". :P