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

Joahn Rowling sagte in a very Kürzlich interview to some Fans that asked her ,the same Frage ,with Du and sagte that Rats are allowed in the school coz of a very ancient tradition in Howarts.Hope I helped you!

Thats a good Frage because in POA Ron sagte the ratte was Percy's first.

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