Pet Owner's Manual (abridged)
Your pet has certain needs you need to fill to make sure that it wants to stay with you. First of all food: it will happily eat beans, because they are magical. You will see when your pet is hungry, but it will eat all the beans that you feed it, even when it is stuffed. And your pet wants to be proud of you, the better it likes you, the longer it will stay with you. Whenever you receive some house points or an award, your pet will know and think you are the best!
You should check on your pet whenever you have time between your studies, pet it and make it feel loved! If you don't then it might become lonely or depressed. Starving or depressed pets might just run away from you, become strollers on the HOL Grounds, or find themselves a new owner. And if they see you not bringing home anything to be proud of in a while, they feel they might be better off with someone else. If your pet runs away, there is no way of getting it back.
We are selling owls, cats and toads, and they are behaving slightly different from each other. Cats have an average size stomach, start with low prestige and average happiness and they cost less than an owl but more than a toad. Owls have the biggest stomach, start with the highest prestige and lowest happiness, and are the most expensive of all. Toads have a small stomach, start with the highest happiness and average prestige, and they are cheap (but they run away easily).