In the Sorcerer's Stone, it says first years are allowed to bring an owl, cat, atau toad. Then why is Ron allowed to bring his rat?

Joahn Rowling berkata in a very baru saja interview to some fan that asked her ,the same pertanyaan ,with anda and berkata that Rats are allowed in the school coz of a very ancient tradition in Howarts.Hope I helped you!

Thats a good pertanyaan because in POA Ron berkata the tikus was Percy's first.

Maybe the owl, cat, and toad are the common ones and they don`t name the unusual ones.