Sario Rips are holes in the space-time continuum that suck in nearby objects and people and then close up. Beings will be transported a day or so back, and they have to get back to their own time (as both times are occurring simultaneously – often someone in one time will have “flashbacks” from the other) and prevent the Sario Rip from occurring. Otherwise, when it ends, the universe will have two of the same person and eliminate them both. The only other way to get back is to die in one time, then snap back to consciousness in the other.
(When Ax learned about them in school, he was distracted by a game later in the day, <and also, there was this female…> which led to the Animorphs being nearly oblivious when Jake was in one.) Understand? Well then I wish you’d explain it to me sometime, Buster.