from testing, red apples increase digestion rate and indigestion by a moderate amount (and while unconfirmed it seems to have minor boosts to weight gained by preds when they digest other things like students and paper as well as other apples)
green apples decrease digestion and have a low indigestion increase meaning you have more RNG time but less chance of RNG indigestion compared to red apples
crazy apples (purple) are rare but increase indigestion by a substantial amount and add a crazy modifier to the pred, making them shake a lot and be unable to eat/keep anything down while the apple is digesting so using one when you are about to leave with the book is a good idea (but with the RNG nature you can still fail if you are in a pred's stomach with this apple as she'll probably vomit everything else out first and leave you in there for 5 minutes and lose all mass to get a vomit RNG tick in the indigestion RNG ticks)
the easiest way to explain that is the pred uses a hitbox right in front of themselves to pick what to eat and the pred also has their "eyes" somewhere in their chest/neck for normal girls and the bottom of the breasts for the fairy thus they loses sight of you if you are directly behind a student at a distance allowing them to "pivot" around a student while searching your last known location (this means she is not actually chasing you while you are behind a student, merely in aggressive investigation mode while the student acts like a wall she saw you go around), the easiest way is to wait till the pred is almost on you on one side then switch to the other for more success in getting them eaten
ie: sit slight right of the student and once she starts chasing sit in the middle, if she loses sight of you then peak on the right again until you are sure she can see you over the other student, then move left to keep the student directly between the two of you for them to be swallowed...it takes a bit to get it in your head but once you do it just becomes muscle memory
below is a diagram of how the pred works if she spots you at the 104/105 elbow on the first floor from 3 different spots, red is her with the red triangle being her vision and light blue being your last known location to her, blue is your current position if you duck back to cover with orange being her target location based on what she saw, the green dot is a student and the funny triangle is a representation of how a student can block her vision at a distance leading to her pivot around them and nab you if you dont pivot to either of the fins at the last second while standing directly behind, so it's much easier to just sit on one of the light blue dots until she is close then pivot to the other dot
Bro yor are a genius, its really handful to know this. Well unless the other student start to run away form the pred too and most of the times they are even faster than me haha.
I just know this little trick about that if you press the Right click you crouch, and for the Left click you run. Don't know if it was intented but I don't see a text in game that tells you
