when an apex pred is chasing you and they bump into a non-oversized, stunned, chasing pred they have something like 30% chance to eat that pred just like how students get eaten
the only exception is tulpy who can be eaten by student preds as well as has no protection from being eaten by another apex, so she is easy to eliminate in 2 pred mode by making her eat a student then having the other apex eat her while she is stuffed and unable to chase you, as her size is 2ish so most apexes and their3-6 capacity can eat her up